(First of all, sorry if I make some mistakes, my native language isn't English)
I've been playing League of Legends since it came out. Trough the years the game improved a lot, always focusing on players desire and community needs.
I have a huge amount of real life friends (and also some that I made in-game) that play LoL, we all share a "tradition", when it's someone birthday we usually congratulate each other offering skins or champions.
Here's my suggestion:
When it's someone birthday, the client could have a notification system or reminder that someone is close to celebrate his/her birthday.
Knowing that, in-game friends could have the option to gift him/her with a skin/champion/RP with a little discount (5%~10%), and Surprise Party Fiddlesticks obviously would be half the price :P
Scams could be avoided with a system that prevents gifting the birthday person if you aren't friends for at least one month, and not being able to change the birthday date.
It's a good way for Riot make people spend money on RP to offer skins/champs, and a huge community interaction idea.
Hope you like it,