I imitated my mentally handicapped coworkers laugh.

I work in this big office building and one of my coworkers has a very distinctive laugh. It sounds like woooOO, and he laughs a lot. He's a nice guy, but people in the office teased him a lot for that, and it was honestly very annoying. One day while I was at my desk and my boss was next to me, my coworker started doing his laugh so I imitated in a woooOO. He immediately stopped and looked back at me, and then my boss looked at me like I was an asshole. The coworker then said "why you laugh like that? I'll be honest, I felt like a total piece of shit. I felt very bad and since then I've been avoiding him at all costs. I'm posting this here today because I'm actually a good guy, but I did something shitty that day. I honestly feel bad now. My coworker is a nice guy, and I feel like he would even forget I did that if I apologized, but I just can't do it.