This didn't happen to me, but my sister, but it was embarassing for her.

So, it was New Year, and we were at my gran's for New Year's Dinner. We brought over the PS2 and a few games - one of them being Dragonball Z: Budokai 2 or 3. Anyway, my sister prides herself on being able to kick most of my family's ass on this game. But, that one time, my younger cousin, Jade - aged 7 or 8 at the time - decided she'd play. The first and second time my sister and my cousin played, my sister was going easy on her - and my cousin beating her wasn't such a shock. BUT the third time, my sister went all out - trying her best, pulling super moves and everything.
My cousin won. And she was just randomly mashing buttons. My sister, who is awesome at the game, was beaten by a 7 year old who's never played this game before in her life. It was so funny.