بگو بخند / begu bekhand
Begu means say and bekhand means laugh. Together it implies that you are having a good time, talking, laughing, etc. For example:
I was walking down the street and I heard a begu bekhand coming from one of the houses. I wonder what they were talking about!
Leila and Behnam talked all night at the party. They were having a real begu bekhand.