My husband and I once attended a christening of the baby of my husbands best friend. It was quite a distance away. We were the only friends to attend. Everyone else was family or home town friends of the mother.
We were younger, so didn't have much spare cash at the time. They knew this. But my husband took the day off work (losing out on pay), and we spent money traveling to the christening.
When we arrived, we were basically blanked by the mothers family, people we had met before! We felt really uncomfortable the whole time. The fathers family, whom my husband had met before, were the only people who spoke to us the whole day. They were lovely.
We spent money on 2 really nice gifts. We were pretty chuffed with our gifts to be honest. We were really happy to be giving them. We thought they would be well received!
We never even got an acknowledgement of the gifts... never even got a "thank you so much for making the effort to come".
To be honest, it was the beginning of the end of the "best friend" friendship. My husband was quite upset about it. Not angry, just upset. Upset about not being acknowledged, and also upset because he realized this friendship was going to fizzle out somewhat.
This was our first experience like this. As I said , we were younger at the time. It still kinda hurts to be honest. So it made me realize the importance of acknowledging/ saying thank you. Since then (and even before, but I'm more aware of it now), I have always made the effort to thank anyone for their gifts / well wishes.
It is rude.