Sarcasm is genetic...really

I have come to the realization that my 9 year old listens much better than I thought he did and very well when we think he isn't listening AND he has inherited this strange sarcastic humor-from where I have no clue. Our younger son had a sleepover last night with the cutest little friend-who happens to be vegetarian. Well the night before hubby and I were joking around (sarcastically) about what to make for dinner, had a good laugh and went to bed. The night of the sleepover arrives and I am getting ready to make dinner, older son gets this gleam in his eye and says, "Hey mom, what are we having for dinner, turkey?". Poor little guest gets this weird look and says "What?". I promptly assured the little guy we were having spaghetti with vegetable sauce-then turned and sent older son to his room for a firm reminder of how to be polite to guests. Aaggggg, nurturing humor with a "filter" is so hard:)