A Walking Wikipedia is someone who appears to have more definitions inside them than the famous online dictionary. They will bring up nuggets of amazing information, usually totally irrelevant to the conversation and totally pointless. They are generally admired by people for their knowledge of pointless facts.
Guy 1: 'So did we have any English homework?'
Guy 2: 'I think so, yeah'
Guy 3: 'Did you know that a pig's orgasm lasts for 30 minutes?'
Guy 1: 'Alright you walking wikipedia, thank you but i'm a little busy right now'