What is Back Titties?
1.
When someone is so fat they have what appears to be tits on their back. Multiple sets are also common.
While walking behind someone to say "Oh my god he's so fat he's got back titties."
See
2.
back fat so big it looks like titties on your back. In some women, they are actually bigger than their real titties.
"Damn those are some big back titties"
See