Diablo, when you click on the cows.
Still unanswered:
Clue: It’s from PC game- one old enough that it ran in DOS.
Clue: Also from a PC game, and one of its sequels or prequels has already been an answer in this thread.
“You look like you need a monkey.”
“Hey! Don’t shoot ME!”
I’m going to guess at Max Payne 2.
I know at the point when Max and Mona team up and you switch between playing them both, you can shoot at the other one and they get annoyed with you for doing so. I don’t remember what they say, though.
The answers to the ones I reposted above are:
“I didn’t mean to call you cannonball-head.”
The Secret of Monkey Island
“There’s only one way to make this right.”
Fallout 2
Good guess, but it dates farther back… anyone else want to try?
WAG : a Monkey Island game, or Metal Gear Solid 4, or The Longest Journey’s sequel.
I’m sure I know that quote from somewhere, I just can’t remember where, dammit !
Three strikes, yer ouuuut!
Redneck Rampage ?
Wow, I never anticipated such an overwhelming response. Sadly, none of the entrants guessed correctly: the game was Beach Head II: The Dictator Strikes Back, a game for the C-64 (and a few other platforms), which—like Impossible Mission—featured some synthesized speech. At one stage of the game, the player must protect wounded prisoners hobbling across the screen by destroying obstacles, such as rolling tanks and bomb-dropping enemies, before they can kill the prisoner. Each time a prisoner was hit by the player’s friendly fire, he’d pause and exclaim “hey, don’t shoot ME!” Which I found pretty funny, and impressive, in 1985.
Also, prisoners crushed by a tank would emit a horrendous death-scream identical to the one used in Impossible Mission when a player falls from the lowest platform—which I also found pretty freakin’ funny, but that was back when I was a black-humored misanthrope, nothing like I am today.
I thought that sounded familiar. One of those was also the game where the bad guy would say “You can’t hurt ME!” Of course you were constantly firing at him, so it came out more like “You can’t hurt ME uh! uh! uh!” as you shot him. 
Yeah, that was it! The Dictator had a bit of a “Black Knight” response to being hit with flung daggers.
Here it is, at about 5:15!
Good times, good times.
“You got a Yoshi Doll! Recently, he seems to be showing up in many games!”
And yes, I had to start a new game to get the quote verbatim.
“Hello, and welcome to the enrichment center.”
Which, I expect to be answered in two seconds.
Since nobody’s gotten mine, I’ll repost it:
‘Oh, snapplecakes!’
Hint - theoretically, he’s on the same side as the main character, but he does everything he can to cause the main character/player problems. That line is just the wackiest example of his generally rather whack dialogue.
Munch? - Oddworld?
This is from Thief: The Dark Project. The actual quote is “Hey, I’m goin’ to the bear pits tomorrow. You wanna come with?”
“Silence the discord.”
Nah, this game came out more recently than Oddworld, later than the most recent instalment, even.
Portal, I think ( which I’ve yet to play, actually ).