Why would a guy at work out of nowhere start picking on me and say randomly a joke while laughing saying 'do you need to get beat up?'?

So i knew him at work (not close just as coworkers loosely) for about a year. Then a few months ago he randomly began to pick on me and annoy me purposefully with his friend. Recently him and his friend were bothering me at the elevator and he said 'do you need to get beat up?' While laughing after i reacted probably with an eyebrow raise.

He also recently stared at me with intense eyes. I never knew he had such a feeling inside him.
Why would a guy at work out of nowhere start picking on me and say randomly a joke while laughing saying 'do you need to get beat up?'?
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