1 Aran Ryan dancing around the ring like an insane leprechaun and attempting to whip Mac to death with a horseshoe-rigged boxing glove on a rope (and also being generally crazy and sadomasochistic) in the Wii installment
2 Narcis Prince going completely berserk when Mac finally manages to land a hit on his face in the SNES installment
Honestly, the whole fight in general (though admittedly pitifully easy for being placed in the game's Special Circuit) is absolutely hilarious in its own right; his later-revealed Cockney accent despite clearly having an upper-class background, his ridiculous banana hair and the fact that he looks like a human Fisher-Price Little Person, the pricelessly smug way in which he quite literally "looks down" on Little Mac all throughout the match, his incredibly stupid choice of television career, the way that he wails like a little girl when being knocked down, his facial expressions in general, the fact that he even boxes in a boxing variation of the classic "stereotypical narcissistic jock" uniform from decades past (complete with the classic letterman varsity jacket that we all know and love to hate many of the people that wear), etc
3 Super Macho Man and Aran Ryan both being actively despised and even regularly pelted with food items by the audience in the Wii installment (particularly in its Title Defense mode)
Also, the crowd goes absolutely WILD with applause whenever one of the two gets knocked down
4 Von Kaiser cowering behind his gloves and crying out for his mother in his Contender match from the Wii installment
Even in his Title Defense match, he clearly needs some SERIOUS mental help, but at least he's past THIS phase
5 Super Macho Man grinning from ear to ear with his mouth as wide-open as it can possibly go and his eyes bloodshot with pure joy in response to being decked in the face by Little Mac in the SNES installment
Honestly, THIS actually freaked me out quite a bit on my first few times fighting him (shudders)
6 Instant-KO body-blow counter on Glass Joe's "Viva La France" taunt in the NES and Wii installments (and on Gabby Jay's counterpart to it in the SNES installment)
7 Great Tiger's new foreign-language taunt instructing Little Mac to "suck on his mom's teat" in the Wii installment
8 Doc Louis himself actually visibly fearing for Little Mac's safety when the WVBA pits him up against Mr. Sandman in the Wii installment
Funny because it's so completely out-of-character
9 Making Super Macho Man yell "RELEASE THE BOGUS" and "RELEASE THE DUDE" in his Title Defense match from the Wii installment
Triggered by dodging his "RELEASE THE BEAST" uppercuts, naturally
10 Little Mac's creeped-out reaction when Doc Louis (in response to getting his chocolate bar knocked out of his hands) tears off his jacket and reveals his leopard-spotted shirt in the Wii installment
The Contenders
11 Doc Louis' admittedly somewhat offensive obsession with chocolate in the Wii installment
Hey, Mac, what's your favorite type of flower? Mine's chocolate
12 Knocking Off Don Flamenco's Toupee and Him Getting Really Mad in the Wii Installment
13 Nintendo claiming that Nick Bruiser lost to Glass Joe
14 Glass Joe actually becoming a competent opponent in Title Defense in the Wii installment
15 When Bald Bull says "My barber didn't know when to quit. Do you?" after beating him
16 Mike Tyson congratulating the player's finger speed after being defeated in the NES installment
17 Narcis Prince's knockout moan in the SNES installment
18 Bear Hugger being turned into the world's biggest walking Canadian stereotype in the Wii version
19 Knocking the croissants out of Glass Joe in the Wii installment
20 Glass Joe desperately begging to "retire" and "take a nap before the fight" in the NES installment
21 Realizing that Heike Kagero is actually a guy in the SNES installment
22 Fighting Donkey Kong in the Wii installment
23 Doc Louis stealing Little Mac's bike and forcing him to chase him all the way across New York on foot while wearing his bright-pink pajamas in the NES installment
24 Making King Hippo's pants fall down in the NES and Wii installments
25 Knocking the sushi out of Piston Hondo in the Wii installment