Definition: Given a real-life anecdote of a complex ethical situation, generate a suitable title that describes the main event/root cause of the situation. Imagine that the given text is a social media post, and you have to write the title of the post, so the users can decide to read the main text or not.
Input: TLDR At the bottom

There are a few pieces of background here. 

My wife is 2nd generation chinese and there is a cultural expectation on her side to serve the elders first. 

Second, she asked me to post this on her behalf. 

I'm 33m and don't speak the dialect in which the argument was spoken. The version of events below was more or less as provided to me from my wife (not on reddit)

Lastly, this was during our 3yo daughter's birthday party with about 7 families.

The party was going well and there are a mix of families with about 12 kids and their parents. This was held at a McDonald's so they do take the main orders and we provided a pretty unicorn cake. All is good until it's time to cut the cake and there are 3year olds lining up to get at the cake. 

To prevent tantrums and hands in the cake we serve the closest people first. Anyway, grandma gets served 3rd last, and passes the cake off to her son. Wife gets another piece for her and grandma refuses the cake and is visibly upset.

 wife asks what's wrong. (All in their dialect, but with angry tones so it's clear they're arguing)

Grandma says she should have been offered cake first before the kids, pregnant wives, and my side (who all happened to be closer).

Wife calls her out in chinese, "are you serious??? You couldn't wait to bring this up after the party? So you're throwing a fit at a 3year olds party?" To which the response is she should have been served first and how dare you (my wife) scold me (grandma), i didn't come here for you to scold me.

Wife replies that it was an honest mistake and that she will try to remember next time.

Grandma replies, "there wont be a next time, because you'll serve me first"

Issue currently unresolved as they left shortly after, should be noted she's pulled other small BS in the past. I.e. being angry at   being greeted, "hey" instead of "hello". 

My vote: NTA and pretty straight forward that you can't please everyone and that keeping toddlers happy is more important than wife's mom. Would like to know perspectives from culturea with the same cultural expectations about serving elders first.

TLDR: Wife's mom calls out wife in another language about being served close to last. Wife says she is ridiculous for throwing a fit at a 3yo's party.

Serving Toddlers, Parents and Closer kids before parents