I love it when this happens, seriously, I always tell the guy with the bad attitude how old, out of touch and completely behind the times they are, I really do just laugh and point at their record crates and smile. I'm a dick when someone gives me attitude, I respond with that kinda "instant karma" attitude, however they treat me is how I treat them, usually right then and there.
look at these moments as a chance to laugh in the face of the childish stupidity of others, its actually really funny when you drop the reverse snobbery on them.
"WOW, you actually dont know what midi or timecode is? where the hell have you been man, playing in the 90's or something, you know that was almost 2 full decades ago right dude?" this is ALWAYS hilarious.