A huge erection, usually caused by an extremely hot chick.
So we were messing around and Jenny took her bra off. Her tits were so nice that my diesel boner popped out of my draws and between her sweater puppets.
An enormous erection provoked by the sound of a Diesel engine. Usually reaching its peak upon hearing the compressor surge. Pointing slightly to the left is a key sign to look for.
It was inevitable that Tyler would end up with a diesel boner while at work after hearing the big Ford leave the parking lot.