A person who always wants to take and not give anything while in the act of having sex. This may be someone who forces his partner for a blowjob, handjob, or positions which requires no participation from this person (Like woman-on-top) and won't do the
honor to satisfy his / her partner.
This comes from the
popular word couch potato, basically describing someone who is
lazy, sitting on the couch and watching TV (yes, without bothering to entertain the TV set once he's done)
Kate: I left Joe 'coz he was such a sex potato, I was completely tired.
Mary:
God, that must be like slavery! Glad you left him. Date an athlete this
time