A makeshift calendar kept in your head so there's no evidence; used to stalk someone you're obsessed with. It is compiled mainly from readily available information made public on social networking sites, and through eavesdropping, lurking, gossip, and rumor.
Jill: You know Brit's gonna be at the party next week, right?
Jack: Oh, for sure. Had that shit marked on my stalker calendar for weeks.
Jill: I have a crush on your friend John...
Jack: Want me to have him add you as a friend?
Jill: No, it's cool...I always know what he's doing. He RSVPs to events, says where he's at in his status, and we have enough mutual friends for me to start a decent stalker calendar.
Jill to Jane: Wanna meet at StarB's Tuesday?
Jane: Yeah, like 8:00?
Jack (lurking ten feet away) to self: Sweet!
Jill: Funny how we keep showing up at the same spots!
Jack: Isn't it?
Jack to self: Thank you, stalker calendar!