O.P.D.
Other Person’s Dick is the guy’s version of Other Person’s Pussy. It’s when someone else’s dick is the main thing you think about.
@jim: 'That guy’s got a nice dick!' (he was distracted for 20 minutes)
Sarah: 'Why is he showing off his dick?' (she was bored)
Mike: 'I’m gonna marry his dick!' (he didn’t know it was a joke)