From the web site:

"It's very hard to stand against hormones overwhelming the constant annoyance realizing that your sis has become a sexy girl: nice firm breasts, long coltish legs, and of course that same pretty face that has much earlier perfected her unique brand of tortured wail."

In other words, Jamie's in charge of collecting all the jock straps. She wants to see if you're wearing yours. Fuck her there in the locker room.