My all time favorite parent/stoner interaction would be my old roomate. After getting good and truly baked out of his gourd, he walks into his parents house with his bubbler still in his hand. Lets reiterate once more for good measure, with his bubbler still in his hand. He stops to pet his dogs, still holding the bubbler. He carries on a conversation with his mother, still holding that damn bubbler. Finally his mother decides to question him about his habits and what he's holding

"So, do you smoke a lot of pot?" she inquires. Clearly feeling more clever then he actually was at the moment, he responds with good, old fashioned stoner comedy:
"Occasionally...I smoke a lot."

It wasn't until he left that he realized the bubbler was still in his hand...