Nickname for the US Air Force B-52 strategic bomber, referred to as a "Big Ugly Fat Fellow" or "Big Ugly Fat Fucker". Considered a term of endearment when used by aviation types.
The NVA types in Hanoi were a bunch of cocky bastards until Linebacker II (major Vietnam War bomber campaign in December 1972). The sight of all those BUFFs rattling their windows on a daily basis was enough to tighten their sphincters good.