To feel annoyed at being left out of a pointless activity?

[Brightredpencil]

I started a new job as a job share 2 years ago with about 10 people I was already acquainted with. They have a Birthday Club where they all add a bit of money in and then each get a Birthday present out of it. However, EVERYONE in the club simply asks for a voucher for a shop to spend (presumably to ensure they get their full money's worth from the club iyswim). It just seems a weird way of passing the same ten pounds around.
I have never been asked to join this club. I work in an office attached to the main office but I go in every day to hand over money, ask about their families etc, drop off work etc. About monthly one of them will come in with the birthday card for another team member, poke their head around the door and visibly deflate when they see me instead of my job share co worker because they want her to sign the card.
AIBU to think they're extremely rude for not inviting me into the birthday club I would probably refuse anyway! and also behaving like they're disapponted to see me?

We dont invite people to join the birthday collections. Everyone knows there is one. If they want to join in they do.

As for the looking disappointed. Yabu. They are looking for someone for a reason and they arent there. Its not that they dont want to see you. Its that you arent the person they needed.

On top of all this, you dont even want to be part of it.

If you want to feel involved. Get involved.

It wouldn't bother me at all, the more daft things like this I can stay out of the better.

I'd be both happy and sad about this. Happy that I didn't have to part with my money but sad that no one had invited me to join and I'd really wonder why.

I think you're being daft.
A real AIBU would be if they were pressuring you into joining a club you couldn't afford.
Good on them for making it truly voluntary.