UAE (and other GCC countries) apply strict Shariah law, so anything that is in contradiction can be interpreted as an offense and means a jail sentence.
You probably get away with most things but if someone decides to throw the book at you - you're as good as toast.
After almost 15 years I have experienced that the most sever things are personal insults (e.g. finger or FU) and insulting the local religion (will not even go there).