mus b nice

Used to convey jealousy towards another person that has something that you do not

Mike: Yo, Kyle I was hitting it from behind last night

Kyle: mus b nice

mus be nice

When your homie starts hanging out/ dating a girl and you are alone

Mark: Damn nathan just hugged that girl
Gian: Mus be nice
John: Mus be nice
Kevin: Mus be nice
John: MUS BE SO NICE