ROOSTER COGBURN from TRUE GRIT (1962) DIRTY HARRY SENTENZA/ANGEL EYES from THE GOOD, THE BAD AND THE UGLY THE LA MOTTA BROTHERS from RAGING BULL TONY MONTANA from SCARFACE all the badasses from EXTREME PREJUDICE (1987) JULES WINNFIELD from PULP FICTION MR.BLONDE/VIV VEGA from RESERVOIR DOGS
Seeing how the whole posse was completely destroyed by Wydell+the Unholy Two (and Wydell would've won had those guys stayed rather than bolt as soon as their job was done) I don't think we need to even look beyond this movie. Snapper made Otis his bitch.
Doug Bukowski from The Hills Have Eyes could handle them. He single handedly took out Cyst and Pluto and kicked Lizard's ass; and they were mutated and had superhuman attributes. The Fireflys are regular psychos. They're not that intimidating.
Grimice-McDonalds Christine-The car Max-Flight of the Navigator Cameron Poe-Con Air The Frog Brothers-The Lost Boys Splinter-TMNT Conner McCloud-Highlander Bill Murray-Space Jam Sub Zero-Mortal Kombat
I DO CROSSWORD PUZZLES IN PEN CUZ IM JUST THAT CONFIDENT
I'm going to leave out all superpowered characters, since that seems to be the vibe of this thread...
The Transporter The Punisher Hannibal Lecter from "Silence of the Lambs" Nick Fury from "Avengers" Black Widow from "Avengers" Lt. Aldo Rain from "Inglorious Basterds" John Rambo Max Cady, from either version of "Cape Fear" Bullet-Teeth Tony from "Snatch" Brad Pitt's character from "Snatch" RDJ's Sherlock Holmes Mad Max from "The Road Warrior" Dexter James Bond Marv from "Sin City" Virtually any character played by either Lee Marvin or Charles Bronson Rorschach from "Watchmen" Nada, Roddy Piper's character from "They Live" Jason Bourne Anton Chighur from "No Country For Old Men"
Keep in mind that most of their victims are FAR from bad-ass. Lots of kids, small-town cops, and other decidedly non-badasses. So the list of characters that could likely take them is going to be large.
They might be the baddest of the bad in this particular film's universe, but they're not uniquely dangerous when you look at the whole of filmed entertainment.