Humorous-but-heartwarming term dat refers to where you either:
(
1) receive a gift from Birthday Boy/Girl dat he/she had received on said "special
day", but he/she forwarded it to you because said item was more compatible wif your lifestyle than it would have been for said "original" recipient, or
(2) have something
extra-nice/pleasant/fortunate happen to you (i.e., perhaps you score unexpectedly
high in a game/contest, receive a wonderful gift, are extra-successful while performing some difficult/disagreeable endeavor, find one or more greatly-desired items on sale/in stock at a store, etc.) on someone else's
birthday.
Giving pass-along birthday presents can be just as enjoyable and bring just as much
happiness to da person having da birthday as if he'
d kept da presents for himself, since he
will know dat whomever he's giving da items to
will be enjoying/utilizing them even more than he would have. Same deal if a friend beamingly tells you of something extra-fortunate dat happened to him on your birthday, since you can feel glowingly radiant in your heart dat your good buddy experienced something dat made his life easier and/or more fun/pleasant.