Any serious attempt at Barleywine or Old Ale. That is to say... I'm fine with "lighter" versions of these, but once you pass 10% alc., my interest wanes quickly. I have no desire to drink, say, a 16% barleywine.
Same goes for top-end Doppelbock and similar. I don't mind a 7% Doppel, but a 11-12% is just unnecessary, I would rather drink six tasty beers with low alcohol content, than drink one beer with the alcohol of a six-pack.
Aside from that? Very little comes to mind. I will brew pretty much anything just to try it out. I don't care if it's sour, weird, or otherwise.