Arby's, Taco Bell...anywhere that serves shredded lettuce.
The worst though is when they combine two or three in one, like KenTacoHut's...KFC, Taco Bell, and Pizza Hut in one. If I want fried chicken, the last thing I want to smell is Mexican or pizza.
The worst combination I've seen is a combo Dunkin' Donuts and Blimpie's subs. Bologna and bavarian cream donuts just do not work together.