For what it's worth (probably nothing), I've never heard the word "bareback" used in this context.
But I have heard the word "bareback" used in another context: gay men having sex without a condom. In particular, gey men who are unfamiliar with each other and who have hooked up, not knowing the other's HIV status. Apparently, the "danger" of having sex like that adds an additional level of "thrill" to the undertaking.