The most amusing death I have ever seen was in Vampire: the Masquerade and as much as I adore the player, I was really glad to see the character go. He deserved what he got but it was a long and winding road.
The character in question's name was Deiros, a Ravnos who had managed to backstab just about everyone he knew to the point that if ANYHTING when wrong it was automatically his fault. My Toreador hated him cause not only did he get her human facade arrested so she lost everything, he eventually blew her up.(She has officially left the game for sanity's sake.)
During the game we came across a 4th Gen Gangrel who we befriended through the pure charisma of a humanity 10 Tremere. Anyway, without us knowing, Deiros essentially sold his soul to her in pieces for information which he then sold on to others.
He eventually unwittingly sold the wrong piece of information to her and when he arrived back, she tore his head off. Literally. What made it funny was the conversation went something like this.
Deiros Player: "I thank her for her time and patience and bow"
GM: "She looks you up and down and smiles"
Deiros Player: "I turn, leave and go back to my apartment"
GM: "No you don't. As you turn around, she rips your head off."
Deiros Player: "Pardon?"
GM" "She. Rips. Your. Head. Off. Find a new character sheet."
I will never forget that moment.
Other not so fun death was my Earth Genasi 12th level monk of Sune in the City of the Spider Queen campaign. She survived everything from the insta-death traps, to the hordes of soldiers, to the giant spider that builds the web briges, to a 80 ft fall but was taken out by a lone black pudding ooze. So bleak that day...