Most establishments nowadays require you to follow certain mandates before you can enter. One of those mandates is always wearing a mask on. You may be denied entry or service by that establishment if you fail to follow the rules, and they’d be well within their rights to do so.
If you’re one of the people that gets mad at these rules, blame the virus, not the people trying to make a living by following government protocols. To the bully that threatened violence for something as flimsy as a mask – you should feel ashamed for acting so despicably!