What does ''can dish it out but can't take it?

It means that a person can tease someone but they can't have someone tease them without getting very mad/upset or without overreacting.

Bob says to Fred, "You're so fat you can't get through the front door."

Fred then says, "You're so dumb you couldn't GET to the front door."

Bob then screams and yells at Fred and tackles him and starts to beat him up.

Bob is someone who "can dish it out but can't take it."