I'd be interested to see my own DPS, I don't care about the damage other players do, though. I don't play any raiding content (except for Alexander Easy), so I don't need to do the biggest of biggest DPS, but I want to do some solid damage; of course.
Thus, I think you ARE allowed to use "fun" as some kind of an excuse and, at least in my opinion, it's okay if you're a casual player (god, I hate that word) and do less damage than all those Hardcore Raiders. Sure, you should know your class, but there's no need to make fun of people due to their damage. With that said, it's okay to friendly ask for trying harder, just don't be harsh or too judgmental.