You don't know what a 3 day wank session is like whilst on meth. Somehow flicking through the most depraved videos online whilst tugging a flaccid knob is endless fun whilst on stims. Ended up with a scabby cock though.
I spent four months on meth last year (and I mean literally every single day, my habit was atrociously expensive by the end) and I can attest to this; my life was basically porn, polish lager and hits of meth all day every day. It never got depraved enough for me.
Stoned sex is amazingly fun if you have the right kind of weed (sativa), but the all time greatest sex drug has to be GHB. You basically haven't lived until you've climaxed in a girl's arsehole while slipping blissfully in and out of consciousness.