What's his deal?

I have a coworker, he seems nice, but hardly ever talks to anyone, but i always notice him staring at me. Last week he actually opened up about it and said he has anger problems, he's super negative and he doesn't want to get too friendly with anyone he works with. I just find it weird though that he watches me whenever i talk to any of my other male coworkers, and seems happy when i notice him or ask him for help ( he's one of the only 2 people that drive the forklift). Wtf is his deal? I dont engage him in conversations out of respect but it's a tad eerie that he watches me when i talk to other males.
What's his deal?
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