I was once in a game where the GM allowed his buddy to be a build like that, but in a nifty "hidden origins" way, where the PC slowly realises their own immense power, but is super clumsy with it, so they're an active danger to the party but you also can't just leave them at an inn because they can potentially destroy the world if they have a nightmare...

Then he got turned into the campaign's secret big bad that was only revealed at the very end. THAT worked out well. Turned out he could control his powers and just used us to get rid of his also evil archnemesis of his before attacking the party.

In half the campaigns, the Doctor Farts PC ends up being the MVP because they weren't minmaxed and as a result have much more utility.

The second one sort of depends on the player. I've had a few players that have made absolutely ridiculous characters but played them very well and it was a good experience.

You mean like the Legend of Poop McDinglefart?