I discussed these topics with some friends and was quite surprised at some of their responses.
Note: Yes means "I'm outta here," no means that you would still be interested in dating them. Also, I am not advocating for or against anything here.
Recreational drug use
Opposite/incompatible party affiliation
Opposite religious views (most notably, they are strongly religious and you're not or vice versa)
Child of divorced/separated/never married parents
Pet allergy/general dislike of pets