lighten up
Intermediate (B1)informal
To stop being so serious and start having fun or being nicer.
"Come on, lighten up — it's just a game, not the end of the world."
Hear it in context

Trump: “Let’s cancel the midterm elections. Ha ha, JK!”
The Daily Show · 2:00
Lighten up.

The Reality Show So Bad It Was Cancelled After ONE Episode
Kurtis Conner · 3:13
Lighten up, pal.

Stormfall Plays Control Resonant (Part 2)
Stormfall33 Vods · 235:40
Dylan, lighten up.

CALL AN AMBULANCE, BUT NOT FOR ME 🚨
UFC · 28:37
LIGHTEN UP LAS VEGAS.

Doc And Marty's Best Friendship Moments | Back to the Future Trilogy
Universal Pictures · 23:57
HEY, LIGHTEN UP, JERK.