Parlance Puns

Last night my dad, brother-in-law, and myself were discussing shop stuff, I was raised on a farm but never really got into the nuts and bolts of farming, machinery, etc. I was trying to name something common in engineering parlance and couldn't quite come up with it. My brother-in-law was also raised on a farm and is big into that sort of stuff, and this line of dialogue ensued:

Dad: "You need to go to engineering school"

Me: "What engineering school did you go to?"

Dad: "H.K."

Me: "What school is that?"

Dad: "Hard Knocks"

Me: rolls eyes