A guy who has two or more relationships that share the same anniversary day or date.
Duder 1: "Dude our anniversary is coming up next week. It's the 14th. What should I get her?"
Duder 2: "14th? You serious? That's the same anniversary as your last girlfriend. You're an anniversary offender doggy."
Duder 1: "Dude don't say anything to her! She would kill me. She hates my ex-girlfriend."