Best thing I ever did was to offer to swap seats so that a lady could sit next to her (adult) daughter.
Oh wait a minute...
Worst thing I ever did was to offer to swap seats so that a lady could sit next to her (adult) daughter and conveniently omit the fact that a small child in the seat behind had persistently kicked my seat for the 10 mins or so since I'd boarded. Her father had been indifferent to the issue saying 'She's a kid and she's bored - what do you want me to do?'.