Drop a brick/clanger
Definition 1 of 1
Pro Tip 1/3British Idiom
This phrase is typical British English and may not be understood by English speakers from other regions. 
She didn't realize it was a British idiom and used 'drop a clanger' with her American colleagues.
Pro Tip 2/3Informal Usage
Use this phrase in casual situations, but avoid it in formal or professional writing. 
During lunch, he admitted he dropped a brick when he spilled the beans about the surprise party.
Pro Tip 3/3Social Blunder
The phrase often relates to a social mistake that makes people feel awkward or embarrassed. 
I dropped a clanger when I asked about her ex, not knowing they had just broken up.