I don't think it always is a faux-pas, and it depends on the recipient and your relationship with them.

Some people believe that cash is an impersonal gift and that you should spend more effort to find a personal gift that the recipient would enjoy. I would find it weird if a friend came to my birthday party and gave me cash, but a gift of a nice whiskey or gin, or a silly joke gift, would feel normal. (Also no gift at all would be fine!)

I've given cash as wedding gifts with the suggestion/hope that the couple spends it on something fun during their honeymoon (but of course they're free to spend it on whatever they like). Plenty of friends who I've talked to have agreed that cash is a fine wedding gift (and sometimes preferred). Most people set up gift registries for weddings, so it's not like the non-monetary gifts from the registry are a big surprise that required a lot of thought and personal attention on the giver's part.

> Anyone who tries to put me down for doing so will simply not be receiving a gift from me next year

Hell, anyone who complains in any way about a gift they've received should fall off the gift-giving list, regardless of what the gift was. Even if someone gives you a gift you don't like or won't use, the gracious thing is to accept it and give thanks. It really is the thought that counts. If you can re-purpose or re-gift it to someone who would actually appreciate it, and do it in a way that won't end up offending the gift-giver, all the better.

I've heard the argument that you should tell the gift giver, because you don't want them to waste their money on something you don't like, but I'm not really persuaded by that. Maybe in some situations, but probably not most. Again, depends on the relationship between the people involved.