"Drinking from the furry cup" is an outdated euphemism for lesbian sex, specifically oral. It stems from the dark ages before women started waxing their pubic hair. These days we take hot wax, epilators and taking blades to our labia for granted but just imagine how disgustingly furry our lady bits would have been just twenty years ago! This is why cunnilingus was not invented until the mid 80s.

These days we associate big hairy bushes with the unkept and raging feminists, which is probably why the furry cup reference has stayed with lesbians for so long.

I'd steer clear of your pen pal unless you want a good shagging.