Yeah I remember watching Dexter's Laboratory at my cousin's house as a kid (the only place I could watch many cartoons as my parents couldn't afford to pay for subscription TV services at the time which meant we only had access to 5 channels - no cartoon network or nickelodeon). He used to call me "Dexter" sometimes. Also used to watch Ed, Edd 'n' Eddy, Angry Beavers, Ren and Stimpy, Fairly Oddparents, Spongebob Squarepants, Invader Zim etc... good times!
I already posted this a while back but didn't really elaborate or explain - I actually wonder if Rigby from Regular Show has aspergers. Even though he is very extroverted and somewhat over-confident in social situations, his social skills still appear somewhat immature/under-developed for his age. He takes figurative speech literally quite often, he seems to have a hard time expressing his own feelings in an appropriate way (as well as actually processing them, in some cases), and he doesn't show empathy for others very often, and when he does he tends to show it in a really inappropriate way that gets misinterpreted - or he simply fails to recognise certain emotions in others and therefore is unable to empathise with them. This is what causes a lot of the problems, confrontations, misunderstandings etc. which are almost an integral part of the show.
He doesn't have much trouble interpreting nonverbal cues from Mordecai like facial expressions and other things, but it's inferred that they've been best friends from a very early age so obviously he'd be very very familiar with Mordecai and could've learned to recognise certain things through years of observation. But, as with all the other characters in the show, Mordecai occasionally misinterprets Rigby's behaviour, too. The misunderstandings can go both ways - it isn't always Rigby's fault.