Funny backfiring Jutsu: Uchiha Sneezing Edition.
Madara doing the Fireball Jutsu, accidentally sneezing mid Jutsu and singing off Hashirama's eyebrows and bangs while they're facing off during a skirmish. (The battle pauses for a moment as everyone processes what just happened. Both clanheads ban talk of it.)
Izuna sneezing during a large-scale lightning jutsu and Tobirama (wearing metal armor and a metal happuri) accidentally becoming a lightning rod and getting struck by a bolt from the sky. (Tobirama goes on to create less conductive armour. He might just have created plastic in general too ...)
Kagami sneezing during Katon practice and it creates a small but explosive puff of fire that singes off his own eyebrows, and possibly also one of his other teammate's as well. (Bonus points if it's Tobirama's eyebrows that get caught in the crossfire at some point.)
