"I once had an attorney offer to handle a copyright infringement case for me and wanted adult videos in payment. Is that allowed?"
Attorneys and clients can certainly agree to a variety of fee arrangements. My only question would be whether the adult videos proposed to be used as payment constituted the copyrighted subject matter of the dispute, that could raise an issue of whether the attorney has impermissibly taken an interest in the subject matter.
"Do you do trademark infringement cases, John?"
Yes.
"what do legal fees equate to in exchange for porno's?"
By an amazing coincidence, I actually had a copyright client offer me free access to pornographic websites in partial payment of a matter I had handled for them. I declined that offer. One might assume that other attorneys would base this sort of fee on the quality and quantity of the screwing provided compared to the screwing received.