This is going to be brief, but it made me laugh and I haven't posted in weeks (DOH!).
According to the Dictionary over at Luciferous Logolepsy, a Rantallion is:
n. - one whose scrotum is longer than his penis
Wow. The english language is truly colorful: there's a whole DICTIONARY of Vulgar Terms. It was compiled in 1811, and that was when "swearing like a sailor" actually meant something. I'm always glad to add another word to my arsenal, especially in the Veiled Insult category.
How did I find this word you ask? Well… I was looking for another word, one that means "out of touch", though the reverse dictionary at OneLook didn't help me this time. I think it starts with an "R", but I can't… quite… remember… what it is. I love having the perfect word, so I spend a lot of time looking at dictionaries, and the online ones are so much faster to use.