What does the acronym pbthh mean? I got it in a text message and I
have found it used through forums and chats but cant find a
definition.

Are you certain that this is an acronym? My first thought is that
'pbthh' may be a way of representing a rude sound that is sometimes
called a 'raspberry'.

A character called Bill the Cat, in the "Bloom County" comic strip,
used to utter a similar collection of consonants:

http://www.mortalwombat.com/Special/BilltheCat.jpg

I'm pretty sure that's a Bronx cheer, a.k.a a raspberry.

Thanks yall. I think that is exactly what it is. That thought crossed
my mind but I wasnt sure about some of the context where I saw it
used. Thanks for the help.