Most on my list have been previously mentioned, some numerous times but here goes anyway:
Football
College: I've been to Neyland many times and it has never improved, other worthy candidates include Davis Wade ('92), Vandy ('92), LSU ('92), Ladd (in Mobile), Legion Field.
Pro: "The Sombrero" in Tampa was just plain awful, so was Fulton County in ATL
Basketball
I've not been to as many so my candidate pool is smaller but the hands down winner would be Beard-Eaves in auburn. The place was horrid, from every perspective: fan, player, sightlines, seats, acoustics, concessions, temperature (had no a/c), etc..., the runner-up, the BJCC before renovations - perhaps even after them.