I wonder if eggplant could set off the test. A portion is only 1% of the nicotine in a cigarette and it's not like many American high school kids are even eating eggplant but it would be kind of funny like Elaine's poppy seed bagels. I know it would be my first excuse in a pinch...I had eggplant parmesan last night!
Tomatoes also contain nicotine. Remember “Tomacco” from the Simpsons?