I ride both, however, I consider myself a mountain biker first and a roadie....last!
I've noticed the different attitudes, so have many of my friends. When I ride the road, other riders barely acknowledge your existence. You might get a quick wave. If they come up behind you, they're trying to blow past you to embarrass you. I you pass them, they jump out of the saddle and grab your wheel. It's a HUGE ego trip.
I love blazing up on my CX (cyclocross) bike to a group, catch them, pull for a bit, then motion I'm turning off and hit a dirt path while they look and wonder what just happened.
When I got mountain biking, I pull up to the parking area, everyone is hanging out talking, chilling, riding other peoples bikes. As I unload, several people ride by, say "hello" and stuff like, "Nice bike"...etc. It's a much more relaxed casual atmosphere. When I see people off the trail with a flat or other repair there are usually 2 or 3 people offering to help.
I don't think riding one form or another makes you that specific type, I think the type of person you are, will dictate what type or riding you prefer.
Don't get me started with Triathletes (or TRY athletes) as I like to call them.
They are the most crybaby, winey, arrogant cyclists that exist.
Of course not all roadies and Tryathletes are jerks, but as a whole, YES THEY ARE!
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"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger