The most thing that makes me crazy about online is delay in withdrawal and kyc requirements, ie failure to verify kyc details when submitted to them and lastly delay delivery of deposit. What I don't really like is after winning and they published your winnings like not secure while dealing online so everyone casino should limit how to publish people's winning.
Apart from the delay in withdrawal there is another type of delay that drives me crazy. When you chat an one representative on an issue that could be resolved immediately from admin, but they will tell you to wait for 48 to 72hrs. For goodness sake it is annoying, just check your admin and solve this problem without making me to wait for another 3days.