Is it disrespectful to pay attention to other things while playing? Sometimes when I'm playing a variation that I'm comfortable with I get bored while waiting for my opponent to move, so I get distracted and start to pay attention to other things around me. 

I know that focus is important, and being distracted can put me on short pants when playing, but lets, for the purpose of this question, ignore that.

As an example, yesterday I was playing with my uncle with no time limit, and the Real Madrid game was on. While waiting his moves I took a (sometimes not so) quick look at the TV.

Obviously, my uncle is someone I respect. When doing this I had (and always have) no intention of looking presumptuous or insinuate the game is easy (and I don't think my uncle got me wrong).

But not everyone I play against knows me as well as my uncle. Does this look bad when playing? Can my opponent be offended?
Whether or not your opponent is offended may depend on your local culture outside of chess, and might also depend on the situation in which you're playing the game. In a tournament with slower time controls, it's not uncommon to even see players get up and walk over to watch other games in progress. On the other hand, if you're just playing a casual game with someone then it's probably polite to pretend you're interested in the current position because otherwise your opponent may think that you don't actually want to be playing with them.