What's the worst decision you've seen a UFC fighter make inside the Octagon?

Paul Daly's extremely late hit on Josh Koscheck

Yeah, bad call. Still went on to have a long career but makes you question what his run would have looked like if he didn't do that. Ferocious power.

Didn't cost him a title but I believe it was Andre Soukhamthath who chose to grapple with Sean O'Malley when Suga was hopping on one leg

Chael Sonnen’s spinning backfist in the Silva rematch. Or his flip over against Fedor. Chael made loads of bad calls actually