This article lists some (minor) exploits that can be activated when combining various hotkeys and actions.
These exploits might not work on some systems or versions.
Also note that depending on the keyboard, some input combinations might not register.
By opening the inventory, holding Forward + Jump, then closing the inventory, you can consistently perform a 0-tick timing (jam).
F3+T is a debug key that reloads all textures and models, which incidentally causes the game to freeze for a couple seconds.
By assigning Forward to T, and by holding T + Jump after using F3+T, you can consistently perform a 1-tick timing (headhitter).