There's a lot of sex had in Friends. A lot of doing the sex. New York's got eight million people in it, but Ross, Chandler and Joey still manage to fall for each other's girlfriends and end up with each other's exes. In a pioneering move nobody's ever done before, we present the FRIENDS MEN'S SEX VENN.
Janice, of course, had an ongoing off-and-on thing with Chandler, and a one-night-stand with Ross.
Charlie originally went out with Joey, but ended up with Ross as they had more in common.
Kathy also went out with Joey, but she and Chandler developed feelings for each other. Both Joey's best friends are jerks, it seems.
(It also means that if Joey really did have VD, they'd probably all have VD...)