How to be able to kill yourself in Garry's Mod

This is how you die

Binding a key to suicide

Basically what you do is go to the console and type in "bind k kill" without quotes.
Then when you are in a game you press the K key and you should die. Easy as pie!

Jumping off a high building or cliff (in game not in real life)

If you are in a map that has some type of edge or building then you can keep jumping off that edge or building until you die. One way to make this easier is to enable realistic fall damage. So if you jump off you immediately die. Super easy!

Typing "kill" in the console

Bring up the console and type in "kill" (without quotation marks). You should be dead when you get out of the console.

Being killed by npcs

Spawn in a crap ton of npcs (make sure they are enemies that can kill you) then just stand there while they shoot at you and you should be dead

Have your friend kill you

Start a multiplayer game and make sure your friend joins. When they join tell them to kill you and they will. Boom! You're dead.

Conclusion

So, there you have it. Those are some ways you can kill yourself! Have fun killing yourself!