Bullets are too slow - Kill a grunt with the crowbar after shooting at him.
Impossible, the only way to knock an enemy upwards is to ragdoll them, which means killing them.
Sleeping on the job stay in one spot for five minutes ( three hundred seconds) without doing anything
References to other valve games
I hate hiking walk ten miles in-game
Pills Here! find every usable medkit in the game
BONK! get fifty kills with the crowbar
there goes ya head mate! get twenty headshots with the crossbow
CRY SOME MORE! fire 32,000 rounds (gluon gun, gauss gun, hive hand, explosives don’t count)
Still Alive fall twenty feet without dying
I don’t blame you knock over ten autoturrets
I’m so glad you felt you had to point out how many seconds were in 5 minutes.
HINT HINT
Looks like your in the barrel today: get in a barrel with a hole in it 
Heh the Icthyosaur one (kill it with a crowbar) should be in. I did that when I first came the Icthyosaur!
Quite fun actually
Over Easy: Kill a Garg, toppling it’s ragdoll, without gibbing it.
Scrambled: Gib the shit out of the Garg.
don’t gargs explode when they die.
They do when the airstrike is called on them. 
in the original hl unless you wasted tons of ammo on a Garg, there wasn’t a single circumstance where a dying garg didn’t gib, so the only death anim is gibbing, because there was no reason for them to spend the effort on something not used.
No matter how a garg in HL1 dies, it gibs.
I screwed around in HLSource and if I recall, they sorta made explosion-sounds, twitched, backed away, turned red, and expanded into oblivion. That may just be the booze talking.
They do all that in vanilla Half-Life also. Except they don’t turn red.
Intern: Beat the game on Easy.
Doctor: Beat the game on Normal.
Professor: Beat the game on Hard.
Ninja!!!: Don’t fall out of the airduct. (the ones the soldiers shoot out)
Sniper’s Bane: Grenade all sniper positions in the game.
OH NO! THAT’S THE CEILING!: Successfully avoid the collapsing ceiling. (Forget about Freeman)
Iron Lungs: Surface just before drowning.
Black Mesa: Swim: Swim for a total of five minutes.
Action Hero: Dive out of the train before it crashes. (chapter immediately after On a Rail, forget the name. Crashes = hits the bottom)
Fast Air: Airstrike the Garg.
Stealth Ninja: Navigate the Blast Pit without alerting the Tentacle.
What do you mean, overcharge?: Suffer a Tau cannon overcharge.
Hey, watch this!: Perform a Tau jump.
Thinks ahead: Launch the Lambda team’s rocket.
If you can’t take the heat…: Fire the test rocket.
Ones I could think of. 
Apologies if any of these have already been suggested, I’m not browsing 33 pages. :fffuuu:
I think a more appropriate title is: “You say jump…”
Hmmm, yeah.
Xen Garden - Take the garden gnome to Xen
Hell, he was in Ep2 and now Left 4 Dead 2. I think Chompski the Gnome needs to appear in Black Mesa too. In a lost and found box in Office Complex or somewhere ridiculously early on in the game.
The tram at the beginning. You should get the achievment by throwing him at the agrunts at the end of the game when you decline G-mans offer.
I don’t have a name for it, but what about :
Go through the whole game using only a crowbar/other necessary weapons like rpg or nades.
I say this because I’ve tried it before.