In the NES game, the only attempt at humor any of the characters make that actually is funny is when Bald Bull says, "My barber didn't know when to quit; do you?"
From the same game there's also Soda Popinski's "I drink to prepare for a fight. Tonight I am very prepared!"
At one point between rounds on the Wii game, instead of his usual advice, Doc tells Mac to remind him to pick up some milk after the fight. It just comes outta nowhere, making it hard not to at least chuckle at it.
"Join the Nintendo Fun— I mean, Club Nintendo today, Mac!"
The original Nintendo Fun Club line was pretty funny and out of nowhere as well.
"What's your favorite flower son? Mine's chocolate!"
More of Doc's great advice: "There are many ways to eat a chocolate, but there is only one way to eat a chocolate bar!"
Decking Narcis Prince in the face can be quite amusing.
Don Flamenco's ridiculously over-the-top defeat animation in the Wii version. He holds up a rose similar to old cartoon characters when they pretended to "die."
Also from the Wii version: Don's anger when you knock off his toupee. The fact that the match had to momentarily stop just so he could react to it is also hilarious.
Mr. Sandman's Title Defense victory cutscene, which has the referee trying to raise his arm in victory, but can't even budge it, and Sandman then lifts his arm into the air with the referee still holding onto it.
Aran Ryan is a walking funny moment in the Wii version. Special mention should go to his fight loading screen, in which he runs around like a lunatic and yells in Mac's ear...without Mac even flinching.
"YA DON'T LOOK IRISH!"
"YA PROB'LY GOT CHEESEBURGERS IN THOSE GLOVES, HAVE YA MAC?"
Bear Hugger in the Wii version bringing in a squirrel to help him box. Every time Bear Hugger gets knocked down, the squirrel comes out and jumps on his stomach to try to get him to wake up.
Doc can't help but fool around when Mac's fighting Donkey Kong.
''Doc: Listen up, son. If you're having trouble...maybe I should call my plumber! Ha ha ha!"
'''Doc: Ok Mac, here's the deal... You go and distract this gorilla! Then I'll go and steal his bananas and make myself a chocolate sundae! Ha ha ha!