Trying to think up a few goofy ones...
Perhaps each puzzle should have one in the first run through of the game, and I believe there is a puzzle where you have to find gears I believe, if so I though up a name for it.
Gotta move that gear up - Solve the <Name> puzzle. (Team Fortress 2 reference?
)
Other goofy ones:
Knocking on Hell's door - Witness an enemy break through a door. (First play-through.)
Eight-legged freak - Find the hidden spider. (I'd imagine an update to the game where the unused spider entity is hidden in a room which the player might easily miss.)
Kiss me! - 'Touch' a Grunt or Brute without them getting the chance to do damage to Daniel.
This isn't Half Life... - Obtain the crowbar. (First play-through.)
Elevation - Reach and use the elevator. (First play-through.) (U2 - Elevation reference.)
And gonna keep thinking of more... You asked for it! >:O