Well next time I'm on a 14 hour flight with you AF_777 I'll remind you not to maintain your policy of keeping your seatbelt on and not to get up to use the toilet or get a drink of water, or something from your bag.
It's all about risk, and even without your seatbelt on, in your seat your at a low risk level. It's more likely mobile objects or people standing up walking around that are going to be affected, including the crew. After hundreds of flights I've never experienced unexpected severe turbulance, and think that risk is low, so I'll still continue going to the toilet etc and accept that one day I might be unlucky.