I’d put it in a box that would be a really nice gift…for somebody else. For instance, you could go get a Hickory Farms gift box, the kind with all the cheeses and sausages, and then use that box to hide the gift he was really hoping to get.
Plus, you get the cheese and sausage, which is very cool if you aren’t getting it in place of what you really wanted!
If you want to be a little impish, give it to him in a box for a “near miss” or even a “total miss” gift:
A box for bath salts and fancy soaps or some other “Mother’s Day” kind of thing.
Another box that might be the right size is one of those sets for installing a water-conservating showerhead. Whoopee! I can have 1/10th the water pressure! What guy wouldn’t want that for Father’s Day!! (Nothing against conserving water, but it would be kind of like giving a mother a high-tech iron for Mother’s Day. If she doesn’t quilt, you probably blew it.)
The only thing is that the gift that would have been in the box has to be something that weighs something close to what you’re actually wrapping, or else something heavier that you could approximate by adding false weight to the package. If you give it to him in a shirt box and the real gift weighs too much more than a couple of shirts and a tie, he’ll catch on too early.
(You can even “accidentally” leave the receipt for the bait gift where he’ll see it.

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