I work in a drugstore, and whenever a kid comes in and awkwardly tells me he wants to buy condoms, I say it out loud enough so that everybody can hear it, to make him feel even more awkward. LOL!
When I was 17 me and my girlfriend were going cross country with her dad over the summer and one day we "fooled around" while he was in a gas station. When he came back out he said "I saw that...", we tried to keep a straight face, so he was confused and said "You two look pretty guilty, I was just kidding!" From then on the trip was really awkward.