A guy i go out with is recently very insistent i keep my hands behind my back. Should i be concerned?

Interesting question, Well i don't really think it's anything g to be overly concerned about. If this were in my case i would most probably get annoyed. Ask him why He likes that certain posture.... ask him HOW you look more attractive..... and I would tell him I don't really like the posture much. Just be yourself anyways he is your boyfriend tell him you don't like it that way. You don't have to abide by everything he says. But if you also feel comfortable or have no problem sitting in that position then keep doing it. But personally i don't find that posture very attractive. my brother used to go everywhere with his hands behind his back he just looked like a nerdy, inquiring old grandpa under arrest HAHA.