I would figure that I’ve been playing too many video games.
I would check if I smell like beer.
I would hit it in the face like everyone else would then I would realize they have metal face plates.
I’d check myself into the Funny Farm.
I would also sneak upon a combine’s back and “neck break” him. 
turn my iPod up a few notches, start playing Pantera, kill it, and take it’s gun.
Then i would run like a mu’fugga
I would walk up to him, look at him in his eyes for a moment, then kick him in the nads. Then I would pour gasoline all over him. Then I would throw a match at him. But since I’m nice, I would piss on him to try and put out the flames. If I succed, I will help him up, look in his eyes, and kick him in the nads again.
If i saw a Metro Cop, I would drop my newly opened can of coke and say ‘‘Pick up the can’’
If I saw a metro cop, (when he is not aware of me), I would kick him in the nuts, folowed with the kick in the face and head bashing to the pavement. Also if he had that shock baton I would zap the shit out of him. Take his uniform and everything he has. Then I would kill a few more deuchebags, hopefully, get a couple of pistols (for the start) and I would make a trale of dead bodies with my dual pistols…
Is there any modification for hl2, that allows dual pistols ingame? Damn, I would sure love that…
Join civil protection and run if I ever see a man who looks like Gordon Freeman. Then make conan96 pick up that can at gunpoint.
Rinse, repeat! 
Why Run away when you can just say the words “Hello! I’m Gordon Freeman!” and he’ll run away saying "SPPPAaaarrreee meeeeeeee!
Or if they havnt met Gordon Freeman yet and your talking about like the 7 hour War, i would run up to him and kick him where it hurts, take his stun stick while hes incapacitated and repeatedly electrocute his metal helmet with it while saying "Dont! shock You! Shock Invade this! Shock Shock PLANET! 
Now i read that it seems kind of harsh, Alwell! 
I would quicksave and try all of the above.
I would shit bricks and then punch him in the face and go away.
There weren’t any Combine Soldiers/Civil Protection Officers in the 7 Hour War.
Regardless, I’d just try not to be noticed, because I’m boring and value my life.
Kill it.
Steal Suit.
Stand in a train station telling people to pick up cans until I get arrested.
I will run away they kill without questioning 
Pick a can and throw it into a trash… can. 
Also, I would probably fill my backpack with cans in case i run into more metrocops…
Since it is one in many way to kill someone unarmed. 
metro cop: shove it, smash its head with a brick, take its pistol/stun stick
solider: find the nearest headcrab
elite: shove its combine BALLZ(particle balls)up its ass
prison guard: so i herd u leik headcrabz?
gunship/chopper: shit a brick
strider: trip it
advisor: eat it