Was Rad mentally challenged?

Especially when he cooked an egg in a microwave.

He was supposed to be shy but I agree with you. The character was border line retarded.

Agreed. I thought his friend Teddy was as well. I was 13 in the summer of 1985 and a year younger than these characters. I was pretty shy and a geek but I certainly knew how to act and respond to other people and how to behave in public. The kids I knew who acted like this rode the short bus and sat at the "special" lunch table in the cafeteria.