The term cotton is reflective of an absorbant material. Much like the term cottonmouth (dry mouth / the mouth which is dry), pussycotton refers to quite literally dry pussy. Which in turn is reflective of pleasure, or in this case a lack there of.
/poos-ee-mouth/ n. Term used discreetly among married straight/bi-curious men to describe any gay male cocksucking connoisseur with a mouth that feels like their wives' pussies used to; the only difference being that this "pussy" satisfies without nagging, having emotions or bleeding, and once you cum, it will leave.
Dude, call Patrick up, that cat has a pussymouth that'll make you nut hella hard!