When Fat Buu rebels against Babidi and kills him:
Goku disappeared and Babidi was yelling at Fat Buu.
Babidi: Just dont stand there your moron!!! Go find and kill him!!! Come on you fat bast*rd!!!
Buu looks extremely ticked off, and comes up with a little plan.
Buu: Oh, master Babidi! I have a plan!
Babidi: Youre too stupid!
Buu: No master, this is a really good one!
Babidi: Fine! What is it?
Buu: First come over here and let me whisper it to you!
Babidi: Very well....
Babidi flies over to Majin Buu, and Buu puts his mouth up to Babidis ear to whisper the plan.
Buu: You see... My plan is......
Then Majin Buu grabs Babidi by the throat choking him.
Babidi: *Gasping for air*
Buu: You see, I know everything I need to know! I no longer need you, and I cant stand you no longer!!!!
Babidis eyes were filled with fear and Fat Buu put his other hand in front of Babidis face...
Buu: Hee, hee...... DIE!!!!!!
Then Majin Buu blasted off Babidis head, putting an end to his cruel master.

Another one of my favorite Majin Buu scenes is when the Pure Evil Majin Buu thinks hell never have candy again, and hes whining about it.

When Fat Buu builds himself a house and he takes you on a little tour, from the kitchen to the toilet!