Not a flavour per se, but any ice-cream that's not a fancy enough brand and is made with crap ingredients (I sound like such a snob!). If it's a good quality ice cream all the flavours will be delicious. If it's not, I'd rather just skip it. Extra hate for things like 'Smartie' ice-cream which tastes dreadful.
Thats only for tubs that you scoop from though as ice-creams in bar form like cornettos and twisters get a free pass, especially if they come from an ice cream van on a hot day!