People (typically North Americans) that are obsessed with British culture, language and comedy.
Your average briteaboo can be found in tea shops, old style candy stores and used book shoppes. They'll often try to use slang such as randy, dashing, 'tis, wanker and tosser. However, more often than not, they don't pull them off.
"Hello there you randy son of a wanker, did you scoff at that episode of Monty Python that aired last night?"
"Bro, stop being such a Briteaboo."