Personally, I don't like it when waiters bring my food without a smile on their face. I notice this particular flight attendant was in a rather dampened mood so I asked her, "Could you do me a HUGH favor!?? Just this once, please!?" Puzzled, she inquired, "What?" And then, I replied, "Could you smile for me just a little..?" She smiles on cue, and patted my shoulder. (It works every time!)