use the lavatory in your ticketed class cabin
Suppose you are in a 737. Row 1 and 2 are 1st class, and you are sitting in row 3. Do you take 2 steps to use the restroom in the front, or walk all the way to the back of the plane? Will flight attendants harrass you if you use the front rest room?
I am curious....is it really a FAA regulation that passengers have to use the restroom in ticketed class cabin?