I sit like that too. When I have a bench all to myself and wanna chill and relax, and don't have to share the bench with anyone.
I don't like being a dick, and calling attention to myself like, look at how wide I can spread my legs, I think I'm the f**king shit or something. Jocks used to do that. I hated Jocks, they were the biggest Poseurs and Biggest Losers in retrospect because they didn't pay any attention.