Birthday surprises. What's the etiquette?

Agreed. It'd save face for her and since you're lying anyways, you won't feel too disappointed at his reaction since you know you're covering for someone else's good intention anyways. Of course inform the girlfriend beforehand so that no awkward misunderstandings pop up unexpectedly. In the meantime, I'd also want to make sure that even if he doesn't think his gf isn't giving him this item, he should think that she has something wonderful up her sleeve for him anyways, regardless of it not being said item. This to be done, so that he doesn't get the wrong impression that one of you is giving him a better gift than the other and also to prevent misconception.

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