Men's Group

an AK-47 makes a better phallic symbol than a Porsche. It's hard-- excuse me-- difficult to see the shape of the gun, and its mode of operation and not think penis on some level. And if you want to insult somebody, genital references almost can't miss, no pun intended. They're very primal. No point of reference needed.

The fact that they're revolting is part of the reason why they make good insults. They, of course, can do some collateral damage, offending people you didn't want to insult. That's why you shouldn't use them. That they'll come out when you lose your temper is almost expected, but you shouldn't use them casually.