It’s rude to be negative at a party.
Brianna just had a horrible day at work and is in a bad mood, but it's her friend Marie's birthday party which she promised she'd attend.
Brianna wants to fulfill her promise to Marie.
Brianna shows up at the party and puts on a happy face for Marie's sake even though deep down she still feels very frustrated.
Brianna attends the party and spends the entire time sulking and complaining.
Marie is very glad that Brianna attended the party and expresses her gratitude towards her.
Marie regrets inviting Brianna and vows to never invite her over again.