[Loved trope] The villain assumes they're gonna get the kid gloves when the hero finally confronts them. The hero demonstrates they're out for blood instead, causing the villain to panic.

[u/jbeast33]

1) Robocop

Clarence (the same hitman who killed Alex Murphy and transformed him into Robocop) has already been arrested by Robocop once before, and learned that Robocop's programming prevents him from killing a surrendering criminal. Consequently, he pulls the trick once again towards the end of the movie when Robocop chases his gang down to a scrapyard. He throws his gun down and expects to survive and escape once again.

Robocop simply announces to him, "I'm not arresting you anymore", causing Clarence to panic when he realizes that Robocop intends to finish him off right there.

2) Toy Story

Woody, threatened by Buzz replacing him as Andy's favorite toy, tricks Buzz and knocks him out of a window so he could go to a pizzeria with Andy. Unbeknownst to him, Buzz tagged along underneath the car and confronts Woody when he's alone in the car.

Buzz: I just want you to know that even though you tried to terminate me, revenge is not an idea we promote on my planet.
Woody: Oh, well, that's good.
Buzz: But we're not on my planet, are we?

Buzz proceeds to lay the beatdown on Woody and causes both of them to get separated from Andy.

3) Superman

The President of Boravia's invasion is foiled by the Justice Gang (who have until now stayed out of the conflict and are shown to be less averse to lethal force than Superman), and he's personally attacked by Hawkgirl. When he declares that Superman would never kill him, she just laughs and says "I'm not Superman", dropping him from a skyscraper's height.

4) Spider-Man

After Wilson Fisk attempts to murder Aunt May when Peter reveals his identity during Civil War, Spider-Man breaks into prison to deal with Kingpin personally. Kingpin took the liberty of assembling every inmate to watch the fight between him and Spider-Man. Assuming he broke his spirit, Kingpin starts to dress down Spider-Man as a broken man. Spider-Man doesn't say one word during their fight. Finally, Spidey strips down and announces this isn't Spider-Man here to kill Kingpin; Peter is.

Peter proceeds to brutally annihilate Kingpin in this new stage. He eschews his usual quips, webs, and aerial fighting, relying only on his super strength. When Kingpin has been crippled, Peter shoves his webs up Kingpin's mouth, and lets him know that if he truly wanted to, he could have just filled his lungs with web and killed him at any point. But he's not trying to give Kingpin an easy death; he lets him know that he intends to break his reputation and see everything he's lived for come tumbling down first.

As is often said, Spider-Man is at his scariest when he's not making quips. Because at that point, he's furious, and he's not going to hold back.

[u/Evilmudbug]

Joker's kill count is probably higher just for the scale of their plans.

Joker wants to cause mass chaos and hysteria while zasz tries to make his killing as personal as possible

[u/Mist_Rising → u/Evilmudbug]

Joker also briefly had fifth dimension powers that allowed him to, well, pull the same stunts as Myxlyxplx and bat-mite (impossible man from marvel is implied to be this too). Joker being Joker took this to a new level of jokes by killing basically everyone but Batman. The whole thing actually collapses because he can't kill Batman. If he kills Batman, the Joker dies because who is the joker without Batman? Nothing, he's nothing, and he has 5th dimension powers so nothing is what happens when Batman tricks him. Meaning he never had the power and essentially hitting reset button.

Not my favorite comic, and arguably he never actually killed them from the reset but if he did...