Too funny, silly, ridiculous, etc. for words
Definition 1 of 1
Pro Tip 1/3Exaggeration
The phrase is often used to exaggerate feelings for effect, not to be taken literally. 
Her story was too ridiculous for words; everyone was in disbelief.
Pro Tip 2/3Humor Context
It's mainly used in humorous or hyperbolic situations, not serious ones. 
His excuse was too silly for words, and it made us chuckle.
Pro Tip 3/3Colloquial Usage
Used in casual conversation among friends, not in formal settings. 
The play was too funny for words, we couldn't stop laughing.