Bad mixer singular noun
Use to describe a person who is not good at talking with other people
As a bad mixer, I find it difficult to communicate with customers.
As a bad mixer, she always feels unconfident to join the party.
A non-alcoholic drink that is badly mixed with alcohol
I think milk is a bad mixer with alcohol.
What are some bad mixers for vodka?
Plural noun: bad mixers
The origin of this expression is not clear.
If you fall for someone's trick the first time then they are at fault.
Are you going to mess with me again? Fool me once, shame on you; fool me twice, shame on me.