I've seen a few with headphones, but since the Cell Phone exploded onto the scene, I see lots of OBS hanging out in the Diner and Cafe glued to their phones.( IINM this is against the rules?)
Are we talking on or off duty? If off duty, I'd let it go. If on duty, but on break I'd tend to let it go, but it is technically against the rules. No offense to those who have previously questioned if it would be okay to sit in the crew lounge, and I know this off topic, but this would be a prime reason of why the crew needs to have a personal space where passengers can't go.