Perfume.
I smell them most places I go, some are worst than others. Some I can't stand. But once when I was in Paneras there was a lady that smelled so horrendously strong that I smelled her perfume in the back of the building near the drinks while she was up at the register. It was unbearable. So I wrote "You smell like shit" on a receipt, told her it was a gift coupon that I didn't want, gave it to her, and left.
Puke/Renuzit air freshener.
We were having trouble with our sewage at my mother's house so I had to sleep on the couch. I was there for about a week, and every night I smelled this horrible aroma that I could never put my finger on. I couldn't tell where it was coming from either so I would get the Renuzit air freshener and spray the fuck around where I was sleeping. On one of the last nights I was there I discovered the smell. In the couch there were cup holders with a piece of wood that slid over them to hid them when you weren't using them. Someone had puked in the cup holders and pulled the wood over them to hide it. I had been laying my pillow, and my head on top of that wood for a week at this point. So anytime I get the faintest whiff of puke or the Renuzit I get sick.