Doesn't bother me at all. Which is good given I travel and I'd go hungry if I weren't comfortable eating in restaurants alone. It's only annoying if I am enjoying a bit of peace, my own thoughts, and/or a good book and the waiter feels a responsibility to form a bond with me since I'm sitting alone lol. Happens more than you'd think.
ETA: I honestly didn't know this was a source of stress for people until I went to college. My random and very sweet roommate freshman year suddenly confessed halfway through the first term that she was skipping lunch some days because she didn't have anyone to eat with and eating by herself was not an option for her. So we arranged to eat together on those days. I enjoy eating with people it just doesn't bother me to eat alone.
ETA: I honestly didn't know this was a source of stress for people until I went to college. My random and very sweet roommate freshman year suddenly confessed halfway through the first term that she was skipping lunch some days because she didn't have anyone to eat with and eating by herself was not an option for her. So we arranged to eat together on those days. I enjoy eating with people it just doesn't bother me to eat alone.