Either I read that one wrong, or its a new one, but Ive gone through half a dozen acronym web sites and what not and couldn't find it.

I've never heard of BTBM, and the Urban Dictionary (a great place to look for definitions), has nothing.

You can always google BTBM, the results include:

Behind the Black Mask - discussion about writers of hard-boiled mysteries.

An construction company from Uzbekistan.

Beacon of Truth Baptist Minitries.

Better Thinking, Better Mathematics.

I can't find anything related to the hobby.  Can you share the context in which you found it?

jazz32

Sometimes with oil, and sometimes with shampoo/soap. It's erotic, and  great foreplay to fucking the life out of one of those little girls.  

AMP= Asian Massage Parlor for the uninitiated.

What do gals say to Merlin when he asked them where he should come?

A:  BTBM  (Between the boobs, Merlin.)

ba-doom

It IS Body to Body massage; came to me in the shower right after I sent this.