funny funny funny joke?

little lad walks into his mum and dads bedroom to find them having sex as the lad gasp his dad turns around and says " ha ha get out you little mucky bugger" the next day as the dad is walking across the landing he hears moans coming out of his sons room when he walks in his son has got his nana on the bed banging away the dad shouts "what the hell do you think your doing you little sh1t" the lad calmly turns around and says "ha ha ha not so fu@$ing funny when its your mum is it"