It's all in the wording. "I don't watch TV," sounds like principle. Like, "I don't drink alcohol." The problem is two-fold. First, it probably isn't true. Second, if it is true it's very likely a sort of idiotic position for the reasons Howard listed. It's not like you have only two choices, watch no TV or spend all day watching Real Housewives and American Idol and The Bachelor.
The thing is, everyone knows this, and they thus know that the person who says, "I don't watch TV," is probably being pretentious and is also probably lying. You can solve this problem easily with a slight change in wording. "I hate reality TV," or, "I don't watch the news," (both of which ought to be true statements for largely the same reasons). Even simply, "I don't watch much TV," is a far better option. You could add a bit of information right up front to take care of the baggage that goes along with, "I don't watch TV." Just say, "I love videogames, so pretty much any time I sit down in front of the TV I'm playing." then you say what you really mean without coming of as puritanical about it.