A towel the size of a large hand towel that you keep handy to absorb "after sex" secretions. A towel that women use after sex to catch semen falling out of their vagina.
Man, after sex with Paul I always have semen dripping down my leg so I have to make sure I have a sex towel handy to clean up.
the towel stolen out of your roomates laundry to wipe off after sex. usually dark in color to avoid detection.
girl: ew you nutted on my belly
guy: shoulda been your face
girl: you're gross. get me the sex towel
<guy grabs towel from roomates dirty laundry and throws it to her>
<girl cleans herself>