When I was a child, my grandfather, a"h, would specifically use whiskey (usually Slivovitz) for Havdallah. Then he would spill some of it onto a plate and douse the candle into the whiskey and watch the dancing flames burn off the alcohol.
I've seen a few people doing this same things since then. Is this a written minhag? Or is this nothing more than just "fun" for kids (and, perhaps, adults, too?)