I would watch for sure. If they saw me I would smile approvingly. Obviously, masturbating, they are also fantasizing a need. I would approach them slowly and guage their reaction then rub my bulging pants then ask if they care if I join them. Slowly, I would undo my pants and expose my hard cock and caress it, not stroke it and would compliment her gorgeous pussy then let things happen from there.
I have always fantasized this happening