diff --git a/src/BizHawk.Client.Common/controllers/ClickyVirtualPadController.cs b/src/BizHawk.Client.Common/controllers/ClickyVirtualPadController.cs
index bc3f223d39..5f2ea15e54 100644
--- a/src/BizHawk.Client.Common/controllers/ClickyVirtualPadController.cs
+++ b/src/BizHawk.Client.Common/controllers/ClickyVirtualPadController.cs
@@ -1,4 +1,6 @@
 using System.Collections.Generic;
+
+using BizHawk.Common.CollectionExtensions;
 using BizHawk.Emulation.Common;
 
 namespace BizHawk.Client.Common
@@ -33,27 +35,9 @@ namespace BizHawk.Client.Common
 		public void Click(string button) => _pressed.Add(button);
 
 		public void Toggle(string button)
-		{
-			if (IsPressed(button))
-			{
-				_pressed.Remove(button);
-			}
-			else
-			{
-				_pressed.Add(button);
-			}
-		}
+			=> _ = _pressed.ToggleMembership(button);
 
 		public void SetBool(string button, bool value)
-		{
-			if (value)
-			{
-				_pressed.Remove(button);
-			}
-			else
-			{
-				_pressed.Add(button);
-			}
-		}
+			=> _pressed.SetMembership(button, shouldBeMember: !value);
 	}
 }
diff --git a/src/BizHawk.Client.Common/controllers/StickyControllers.cs b/src/BizHawk.Client.Common/controllers/StickyControllers.cs
index 6baef48d69..49d1eedca4 100644
--- a/src/BizHawk.Client.Common/controllers/StickyControllers.cs
+++ b/src/BizHawk.Client.Common/controllers/StickyControllers.cs
@@ -1,6 +1,7 @@
 using System.Collections.Generic;
 using System.Linq;
 
+using BizHawk.Common.CollectionExtensions;
 using BizHawk.Emulation.Common;
 
 namespace BizHawk.Client.Common
@@ -37,16 +38,7 @@ namespace BizHawk.Client.Common
 		public void SetHapticChannelStrength(string name, int strength) => throw new NotSupportedException();
 
 		public void SetButtonHold(string button, bool enabled)
-		{
-			if (enabled)
-			{
-				_buttonHolds.Add(button);
-			}
-			else
-			{
-				_buttonHolds.Remove(button);
-			}
-		}
+			=> _buttonHolds.SetMembership(button, shouldBeMember: enabled);
 
 		public void SetAxisHold(string name, int? value)
 		{
@@ -74,14 +66,7 @@ namespace BizHawk.Client.Common
 		{
 			foreach (var button in buttons.Where(button => !_justPressed.Contains(button)))
 			{
-				if (_buttonHolds.Contains(button))
-				{
-					_buttonHolds.Remove(button);
-				}
-				else
-				{
-					_buttonHolds.Add(button);
-				}
+				_ = _buttonHolds.ToggleMembership(button);
 			}
 
 			_justPressed = buttons;
diff --git a/src/BizHawk.Client.EmuHawk/Input/Input.cs b/src/BizHawk.Client.EmuHawk/Input/Input.cs
index 3b20a9977e..9a692e5e41 100644
--- a/src/BizHawk.Client.EmuHawk/Input/Input.cs
+++ b/src/BizHawk.Client.EmuHawk/Input/Input.cs
@@ -20,8 +20,7 @@ namespace BizHawk.Client.EmuHawk
 		/// </summary>
 		public void ControlInputFocus(Control c, HostInputType types, bool wants)
 		{
-			if (types.HasFlag(HostInputType.Mouse) && wants) _wantingMouseFocus.Add(c);
-			if (types.HasFlag(HostInputType.Mouse) && !wants) _wantingMouseFocus.Remove(c);
+			if (types.HasFlag(HostInputType.Mouse)) _wantingMouseFocus.SetMembership(c, shouldBeMember: wants);
 		}
 
 		private readonly HashSet<Control> _wantingMouseFocus = new HashSet<Control>();
diff --git a/src/BizHawk.Client.EmuHawk/tools/HexEditor/HexEditor.cs b/src/BizHawk.Client.EmuHawk/tools/HexEditor/HexEditor.cs
index 67dda4c144..52cb5362a3 100644
--- a/src/BizHawk.Client.EmuHawk/tools/HexEditor/HexEditor.cs
+++ b/src/BizHawk.Client.EmuHawk/tools/HexEditor/HexEditor.cs
@@ -2085,13 +2085,9 @@ namespace BizHawk.Client.EmuHawk
 						{
 							ClearHighlighted();
 						}
-						else if (_secondaryHighlightedAddresses.Contains(pointedAddress))
-						{
-							_secondaryHighlightedAddresses.Remove(pointedAddress);
-						}
 						else
 						{
-							_secondaryHighlightedAddresses.Add(pointedAddress);
+							_ = _secondaryHighlightedAddresses.ToggleMembership(pointedAddress);
 						}
 					}
 					else if ((ModifierKeys & Keys.Shift) == Keys.Shift)
diff --git a/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.ListView.cs b/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.ListView.cs
index 0b49666a2b..12785bf0e6 100644
--- a/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.ListView.cs
+++ b/src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.ListView.cs
@@ -992,14 +992,7 @@ namespace BizHawk.Client.EmuHawk
 						TasView.SelectRow(i, _selectionDragState);
 					if (AxisEditingMode && (ModifierKeys == Keys.Control || ModifierKeys == Keys.Shift))
 					{
-						if (_selectionDragState)
-						{
-							_extraAxisRows.Add(i);
-						}
-						else
-						{
-							_extraAxisRows.Remove(i);
-						}
+						_extraAxisRows.SetMembership(i, shouldBeMember: _selectionDragState);
 					}
 				}
 
diff --git a/src/BizHawk.Common/Extensions/CollectionExtensions.cs b/src/BizHawk.Common/Extensions/CollectionExtensions.cs
index 934e5ad109..775be9d8f4 100644
--- a/src/BizHawk.Common/Extensions/CollectionExtensions.cs
+++ b/src/BizHawk.Common/Extensions/CollectionExtensions.cs
@@ -377,6 +377,30 @@ namespace BizHawk.Common.CollectionExtensions
 			=> source.OrderByDescending(ReturnSelf);
 #endif
 
+		/// <returns><see langword="true"/> iff any removed</returns>
+		public static bool RemoveAll<T>(this ICollection<T> collection, T item)
+		{
+			if (collection is ISet<T>) return collection.Remove(item);
+#if false // probably not worth it, would need to benchmark
+			if (collection is IList<T> list)
+			{
+				// remove from end
+				var i = list.LastIndexOf(item);
+				if (i < 0) return false;
+				do
+				{
+					list.RemoveAt(i);
+					i = list.LastIndexOf(item);
+				}
+				while (i < 0);
+				return true;
+			}
+#endif
+			if (!collection.Remove(item)) return false;
+			while (collection.Remove(item)) {/*noop*/}
+			return true;
+		}
+
 		/// <inheritdoc cref="List{T}.RemoveAll"/>
 		/// <remarks>
 		/// (This is an extension method which reimplements <see cref="List{T}.RemoveAll"/> for other <see cref="ICollection{T}">collections</see>.
@@ -423,6 +447,20 @@ namespace BizHawk.Common.CollectionExtensions
 			return true;
 		}
 
+		/// <summary>
+		/// if <paramref name="shouldBeMember"/> is <see langword="false"/>,
+		/// removes every copy of <paramref name="item"/> from <paramref name="collection"/>;
+		/// else if <paramref name="shouldBeMember"/> is <see langword="true"/>
+		/// and <paramref name="item"/> is not present in <paramref name="collection"/>, appends one copy;
+		/// else no-op (does not limit to one copy)
+		/// </summary>
+		public static void SetMembership<T>(this ICollection<T> collection, T item, bool shouldBeMember)
+		{
+			if (!shouldBeMember) _ = collection.RemoveAll(item);
+			else if (!collection.Contains(item)) collection.Add(item);
+			// else noop
+		}
+
 		public static ReadOnlySpan<T> Slice<T>(this ReadOnlySpan<T> span, Range range)
 		{
 			var (offset, length) = range.GetOffsetAndLength(span.Length);
@@ -447,6 +485,18 @@ namespace BizHawk.Common.CollectionExtensions
 			=> list.ToDictionary(static kvp => kvp.Key, static kvp => kvp.Value);
 #endif
 
+		/// <summary>
+		/// if <paramref name="collection"/> contains <paramref name="item"/>, removes every copy;
+		/// otherwise appends one copy
+		/// </summary>
+		/// <returns>new membership state (<see langword="true"/> iff added)</returns>
+		public static bool ToggleMembership<T>(this ICollection<T> collection, T item)
+		{
+			var removed = collection.RemoveAll(item);
+			if (!removed) collection.Add(item);
+			return removed;
+		}
+
 		public static bool IsSortedAsc<T>(this IReadOnlyList<T> list)
 			where T : IComparable<T>
 		{
diff --git a/src/BizHawk.Emulation.Cores/Waterbox/NymaCore.Settings.ComponentModel.cs b/src/BizHawk.Emulation.Cores/Waterbox/NymaCore.Settings.ComponentModel.cs
index 44f1b88b0e..9c137f9bfd 100644
--- a/src/BizHawk.Emulation.Cores/Waterbox/NymaCore.Settings.ComponentModel.cs
+++ b/src/BizHawk.Emulation.Cores/Waterbox/NymaCore.Settings.ComponentModel.cs
@@ -2,6 +2,9 @@ using System.Collections.Generic;
 using System.ComponentModel;
 using System.Globalization;
 using System.Linq;
+
+using BizHawk.Common.CollectionExtensions;
+
 using NymaTypes;
 using static BizHawk.Emulation.Cores.Waterbox.NymaCore;
 using static BizHawk.Emulation.Cores.Waterbox.NymaCore.NymaSettingsInfo;
@@ -418,12 +421,7 @@ namespace BizHawk.Emulation.Cores.Waterbox
 		}
 
 		public override void SetValue(object component, object value)
-		{
-			if ((bool)value)
-				((NymaSettings)component).DisabledLayers.Remove(LayerName);
-			else
-				((NymaSettings)component).DisabledLayers.Add(LayerName);
-		}
+			=> ((NymaSettings) component).DisabledLayers.SetMembership(LayerName, shouldBeMember: !((bool) value));
 
 		public override bool ShouldSerializeValue(object component)
 		{