A "know-it-all" or "Cliff Clavin". Someone who considers themselves to be an expert on everything. A human storehouse of useless trivia, often of dubious veracity.
"That guy is so wikipedic...full of useless information and he never shuts up!"
"Why did I bring that up in front of so-and-so? I thought I'd never hear the end of it from Mrs. Wikipedic."
know-it-all Cliff Clavin