Show actually jumped the shark imo when Lisa and Will didn't end up getting married and her dad and Will's mom ended up supposedly getting married at the end. And after that, the last season was
Yeah, if we're going to talk about Fresh Prince jumping the shark, then it starts with that episode. I don't know what they were thinking with that ending.
Then the last season had Will act like a cartoon character to the point where people didn't even want to be around him, Ashley reaching her peak of being an a$$hole, Will and Uncle Phil getting arrested on Thanksgiving for hanging around prostitutes, murderous clowns, Ashley turning into a little a$$hole, Will getting made fun of for losing to a boxing instructor, a horse episode, Will and Carlton getting high on laughing gas with William Shatner, and Ashley becoming the worst character on the show.
I don't think Fresh Prince jumped the shark, but it's obvious that if it had gone on longer, it would have become an embarrassment to watch. Will kept the show's legacy intact by ending it when he did.