My mom found a bag in our backyard that had some leaf/seed in it, and blamed it on me. My response, "Mom, if there is one thing you'll never find in a bag of weed that I buy, it is a seed... There is no way in hell that is mine."
Once my friends dad found some bud in his car and my friend was like "Dad if there was weed there, I would've already smoked it" and his dad said "ok".