Hidden flask in a tie
The thing with gag gifts is that they are all about the giver not the receiver.
Imagine the scene:
It's the office secret santa. You're all swapping gifts.
You chuckle to yourself as your co-worker excitedly unwraps their present.
'What is it!' he exclaims 'oh a tie!'
He looks confused (why would you just get him a tie for secret santa?) You smile knowing that you are about to reveal the tie's true purpose.
'It's not just any tie' you say. 'It's got a flask in it, so you can drink from it!...'
Wow. What a great present everybody agrees.
Your coworker tries it once and then it gets buried in his cupboard, never to be used again.
Or perhaps he goes home and cries himself to sleep, thinking everybody in the office thinks he is an alchoholic.
But who cares, you got the glory. Today with the Flasktie you won.