The most boring and absolutely lamest way to checkout early is by getting an explosive (like an RPG or Grenade) and blowing yourself up (unless you are roleplaying as a muslim) or by pressing ~ and typing kill or pressing ~ and typing something like bind _ kill so like bind k kill but we are not here for the boring ♥♥♥♥ are we?

Alright so this will be a slight bit more complex but you need the killbind which was mentioned in the boring section and if you don't know how you are either blind or retarded but knowing the Garry's Mod community you are probably both but anyways you get a killbind by pressing ~ and typing bind _ kill so like for example bind k kill then get yer good ol' crossbow and get to a ceiling that's low and time it just right where you shoot the crossbow at the ceiling and killbind at the same time and if you do it correctly you should have done le epik sewerslide!!!