A sack sniffer can refer to heterosexual and bi sexual woman, bi sexual men, and transgendered individuals who enjoy place their noses up against a man’s testicles.
I take being called a sacksniffer as a compliment because I love to sniff sacks!
A person who doesn't realize they are transgender yet, or is in denial; an undeveloped transgender person. When they realize, it's referred to as the "egg cracking."