from the latin word "porn" meaning 2 or more adults engaged in sexual activities of various deviant nature (depending on what you pay for) and "athon" meaning at least 6 hours worth if you can hold out that long.
damn...just been through a pornathon and I'm fucking exhausted...who was that man? Six hours is just too much...
a porno marathon,watching porn for many hours straight.
man i did a pornathon last night and i swear i knocked out ten batches in 6 hours.