When my DD receives presents she always expresses her gratitude by saying something like "Cool" or "Awesome" enthusiastically (doesn't matter if it's socks or video games, she always acts equally grateful).
A relation in her 60s has complained about it saying that they want a "proper" thank you actually including the words "thank you".
It's trivial so we've asked DD to do it though DH and I are toying with the idea`of bellowing COOL! when we get our gifts.
Just wondering what other people think, does it matter how gratitude is expressed as long as it's genuine or is our relation a misery guts being a bit picky?