A slipper is a vagina, a pussy, that warm little pocket found between the legs of the fairer sex!
Girl: "You fancy a slipper tonight?"
Boy: "Yep, yours? Or someone elses?" (while winking!)
Girl: "Were you looking for a pair of slippers?"
Boy: "Now that you mention it, sounds like fun!"
This is an ancient word dating back to... blimey, must be 1981! Anyway, enough reminiscing!
I believe the meaning to be the crossing of wee strains that go all over the toilet edge, or seat if you didn't put it up.
This was until recently limited to men, but I have discovered, much to the horror of you ladies out there, that Pissel does and can occur when you go too! Round the front of the toilet seat where it must deflect off the pan or something.
Mum: look at this mess!
Boy: what? I can't help it, it's just my pissel
Girl: you've pissed all over the seat again!
Bloke: No I haven't.
Girl: There's piss all over the front of the seat?!
Bloke: That's you you silly girl, it's your pissel