There are several elements that don't change based on the characters fighting that can get a little weird sometimes.
Chiaotzu's ultimate attack, "Goodbye Mr. Tien", has Tien randomly screaming Chiaotzu's name in the background during the explosion. Partially because of this, the attack name takes on a whole different meaning when Tien's your opponent...
Every character in Dragon Sim mode in 3 has the same possible events that are randomly drawn from. Yes, Chi-Chi is ordering the likes of Frieza, Broly, and Omega Shenron to sit down and do their homework.
The Saibamen's ultimate attack leaves the opponent in Yamcha's classic, trademark pose regardless of who it is. It's quite an unusual sight to see the likes of Broly, Omega Shenron, and SSJ4 Gogeta crumpled up and helpless on the ground.
If you or your opponent is a Dragon Ball player or Mr. Satan, expect them to flailing their arms or feet when they can't maintain their altitude on flight-level with someone who can fly indefinitely.
If you linger long enough in BT3's Versus menu, you may hear this quip from Nappa: "Hey Vegeta, you think if I went Super Saiyan, my goatee would turn blond?"
In Ultimate Tenkaichi, picking the "Crazy" voice option for your character in Hero Mode results in some pretty hilarious lines and sound bytes from the Hero. And even when he DOES say something relatively serious, his thick New York accent makes it very difficult to take him seriously.
In fact, depending on which voice you pick, almost any scene can come across as comedic.