Be careful what you say when you're on a plane. We all know free speech is not an absolute; Justice Oliver Wendell Holmes' argument about "falsely shouting fire in a theatre" is Exhibit A. There are also things you cannot say on a plane; doing so may not land you in front of the Supreme Court but it could get you kicked off your flight. There are millions of variations of this joke, but none of them are funny, not in airports and not on planes. The TSA has had to pull many such comedians out of security lines and occasionally arrest them; it happened to an NFL player last year. Frontier Airlines has allowed tipping on the food and beverage sales by flight attendants for the past three years -- tips that were then pooled with the rest of the crew.