Ron White Bar Story Question

I guess he is teasing that different sizes fit him in different stores, which is quite funny since these sizes are not "imaginary" or unique, but universal..

Those who don't like Futurama: Beat it!

He's making a joke that convenience stores have a height chart next to the doors so that the clerks can give more accurate descriptions of criminals. In his joke his height depends on how accurate the charts are.

Satan is a little man