A good/bad mixer
Definition 1 of 1
Pro Tip 1/3Social Context
This phrase is used in situations where someone's ability to interact in social settings is being described. 
At networking events, Amanda is a bad mixer; she finds it hard to join conversations.
Pro Tip 2/3Emotional Nuance
Use 'a good mixer' to imply someone is warm and approachable. 'A bad mixer' suggests discomfort or shyness in groups. 
Despite his expertise, the professor is a bad mixer, often avoiding social gatherings.
Pro Tip 3/3Personality Insight
Calling someone 'a good/bad mixer' hints at their underlying personality traits. 
Even in a crowd of strangers, Marie is a good mixer, always finding something to talk about.