holy crap dude, you're hyper extending like crazy.... if your elbows are going past your back so the bar is hitting your chest, say goodbye to your rotator cuffs and hello hospital bill and agonizing pain. Seriously consider getting someone with good form to teach you the proper way because no one here wants to see you go through that, lol. I'd recommend working out with considerably less weight with and learning good form.
and pec flys are probably a better workout anyway, much less dangerous and just as good (i.e. you're not holding a bar with 180 pounds over your throat
)
sorry if i sound like a prick btw, i don't want it to come out that way