Oh Cave Johnson, I wish I knew you:
"Those of you who volunteered to be injected with praying mantis DNA, I've got some good news and some bad news. Bad news is we're postponing those tests indefinitely. Good news is we've got a much better test for you: fighting an army of mantis men. Pick up a rifle and follow the yellow line. You'll know when the test starts."
"Science isn't about why - it's about why not. You ask, Why is so much of our science dangerous? I say, Why not marry safe science if you love it so much? In fact, why not invent a special safety door that won't hit you in the butt on the way out - because you are fired."
"All right, I've been thinking, when life gives you lemons, don't make lemonade! Make life take the lemons back! Get Mad! I don't want your damn lemons! What am I supposed to do with these? Demand to see life's manager! Make life rue the day it thought it could give Cave Johnson lemons! Do you know who I am? I'm the man whose gonna burn your house down - with the lemons! I'm gonna get my engineers to invent a combustible lemon that'll burn your house down!"
In retrospect, not really a one-liner, but dammit Cave Johnson is too good for mere one-liners.