In my intro to media studies course at my university we had a group project where you were assigned a popular topic in mainstream media and had to rate each form of media based on how likely that topic was to become popular on the aforementioned form of media if it ONLY existed on that form of media. My partner was an ultra hot chick who I haven't seen since that semester, and the topic for my group was Kim K's sex tape. My partner rambled on for at least 10-15 minutes about the tape ending all her sentences with "right?" or "don't you think so?" Now, I couldn't give any less shits about Kim K or the glorified (mandatory) philosophy class we were in, but the professor was walking around the classroom listening in on everyone's discussions so I couldn't just stare into space and not talk to my partner. Sooooo for her entire rant I was basically staring right into her eyes and saying "mhmm" every 30 seconds or so. Whenever she'd look away for a second I'd sneak a peak at her chest. I'm a pig I know, but I regret nothing.
TL;DR: If it's a girl I look her in the eyes unless there's something else worth looking at, and if it's a guy I do the same, but glance at his crotch every now and again to make sure he's not getting aroused when talking to me. Not that I would blame him