How to Drive a Semi...

I have mentioned that Blaine will not let ANYONE drive his new combine, tractor and grain cart.  He always tells anyone that asks that they can drive the semi only.  My parents came over this weekend and Dad tried pretty hard to get to drive the combine.  But, as with anyone else, Blaine only told him that he could drive the semi.  But Dad played along and replied that he didn't know how to drive a semi.  Blaine just gave him a blank stare (i.e. - how stupid are you Grandpa that you can't drive a semi???) and just told him, "You put your hand on the top and push it!"