Got a text from a friend recently who was ashamed to admit he'd avoided sitting with a coworker who he knew was headed his way at lunch.
Making awkward small talk with coworkers or discussing what I'm working on is NOT taking a break. If I'm talking about work, it's still work. If I'm concentrating on being politically (and grammatically correct) during our conversation, I'm still at work.
Particularly when you're fresh on the job, you're strongly advised to sit with new people every day in the lunchroom to meet folks from different cross functional departments and build rapport and whatnot. And I've also been told not to sit with the same people (read:black people) every day. OK, I can roll with that.
But sometimes you don't feel like sitting with any people! Is that selfish? Don't take it personal, it's just that I have to see you for the other 7.5 hours of my shift; I'd like these measly 30 minutes to my self!