Smoking, which is a disgusting, unhealthy habit that I absolutely fucking despise.
Being disrespectful towards me. The whole "unexpectedly bringing a friend along" thing falls under that to me.
Noticeably bad hygiene. If I'm repulsed by their odor and generally have the appearance of not bothering to put in the bare minimum for cleaning and grooming themselves, forget about it.
Being superficial, overtly ignorant, and intellectually shallow. Someone who thinks reading is for geeks and that the Keeping Up with the Kardashians is the height of entertainment is not likely to garner my interest. Anti-vax views and other assorted science-denying nuttery would be right out.
Expression of racism, bigotry, extreme political views (esp. of the conspiracist or far-right variety), or fundamentalist religious beliefs would automatically disqualify them as a prospective mate.