My D&D is pretty serious, which allows for much more relaxing and joking around than the way I run most other roleplaying games, i.e. my horror campaign was treated as DEADLY SERIOUS business (when it was in HERO System for the first two or so seasons before it moved to Delta Green, players even got bonus CP for protecting the mood if they had gone the entire session without joking or laughing; this rule was scrapped when the table basically explained to me that laughter is a DEFENSE MECHANISM against horrible things, and without that defense mechanism, the campaign was too upsetting: I took this as a compliment, but I softened the 'no laughing' rule).
I would say roughly 85% of roleplayers seem to prefer a more relaxed, more goofy, less serious gaming atmosphere than I do. I definitely take this stuff more seriously than average. My goal is to hit as close as I can to the tone and quality of a prime time (HBO) hour-long drama series for each game session. It is a tough goal to hit and I don't always hit it, and maybe impossible now that I've lost the gaming group that I had for more or less my entire life, and am playing with acquaintances and strangers, often in public spaces (FLGS) where I can't control the atmosphere (light, music), but it's still the best way to define what I'm aiming for.
I guess the last thing I have to say is that I am WAY more okay with character-based/in character humor than out of character goofiness. Like if a character does or says something that cracks the table up, I'm fine with that in D&D. It's when the rest of the table starts riffing on it with their own jokes that it gets disruptive IMO.
Oh, one more thing. I am definitely my own enemy sometimes in my quest for seriousness. In that I understand the temptation to joke around and fall prey to it myself more often than I'd like.