I gave mine at departure as it was not meant as a bribe (though if they had moved me up into F on the 777, I sure would not have minded), but as a thank you for all the fine service over the years, "covered" under the auspices of recognizing a day when they could not be home to be with their families and children (since all but two or three of my cabin crews were female).

I usually do the same for my Thanksgiving morning mileage run (I do SEA-SFO-IAD overnight on Wednesday and come home IAD-SFO-SEA Thanksgiving day morning).