Not know whether to laugh or cry
Definition 1 of 1
Pro Tip 1/3Mixed Emotions
Use when feeling a strong blend of contradicting emotions, and you're puzzled about how to express them. 
After watching the bittersweet ending of the movie, I didn't know whether to laugh or cry.
Pro Tip 2/3Unexpected Situations
Best used in scenarios that are so absurd or unusual that they trigger conflicting feelings. 
He painted his house rainbow colors; I didn't know whether to laugh or cry.
Pro Tip 3/3Hyperbolic Expression
It's an exaggeration to stress the emotional confusion and isn't always taken literally. 
She arrived at the party in a chicken costume - I didn't know whether to laugh or cry.