a good mixer

1. Someone who is able to converse easily and pleasantly with other people in a social setting or event. I was worried about bringing my new girlfriend out to a party with so many people she had never met before, but luckily she's a really good mixer. I used to be really shy, but I've become a good mixer over the years. Valerie, the host, is a really good mixer, so I think you'll feel right at home at her party.

2. A non-alcoholic beverage that pairs well with a particular type of alcohol. I turned my nose up when he started pouring tomato juice into the glass, but apparently it's a really good mixer with vodka. Let that be a lesson going forward—milk is a not a good mixer with gin. A: "Do you think energy drinks are a good mixer with alcohol?" B: "Alcohol and caffeine seems like a dangerous combination to me."

a good/bad ˈmixer

a person who finds it easy/difficult to talk to people they do not know, for example at a party: Whoever we appoint for this position will be dealing directly with our clients. We are looking for someone who is friendly, a good mixer, reliable and practical.