I thought about this a lot as a kid, and here's the skinny on it. Like Mogu said, with your left foot flat on the floor set your right leg (about 4 inches above the ankle) on top your left knee, and lean back in a relaxed way with your arms crossed. With your leg up like that you have opened up the crotch and given lots of room for that thing to hang down and be free. The key is the relaxed look, where your comfortable with your surroundings, and with who you are as a person. But don't do this in a meeting or during a formal occasion because it can make you look a bit pompous, or "full of yourself". Especially if it's overdone while your supposed to be paying attention to what's going on. This also takes up more space on a sofa, bench or chair, and it makes you appear a bit more confident when your talking to someone. (if your trying to do that sort of thing). And remember, it's not a sexually attractive pose, just a masculine way of sitting comfortably.
Warning. Watch out for problems when you're wearing loose shorts while doing this leg up routine. We were once throwing lit firecrackers at each other inside our farmhouse, and one fell down the loose leg of my shorts. It blew up just next to my sack, and luckily I was wearing a good pair of briefs. Felt like I'd been kicked by a horse, and there was a big burn mark on the right edge of my crotch. We'd get pretty stupid when drinking.
K
