Okay, so I'm thinking of switching over to a mess bag but I was worried about it slipping around to the front and such (of course, the only one's I'd ever seen were the stupid laptop-esque courier bags at the big W) so I had no idea, checked out timbuk2, and found out a REAL bag (I guess) has a second strap. But the way she puts it on it looks like if I were to have something heavy on it and hit a pot hole or drop off a high curb it'll rip my breast off! Scary! Is it as bad as it looks, or does it not budge at all?