Wiktionary
n. Someone who only drinks alcohol when with acquaintances who are drinking.
WordNet
n. someone who drinks liquor repeatedly in small quantities [syn: tippler]
Usage examples of "social drinker".
He said Tuckerman had been a heavy drinker for years, thinking of himself as a social drinker but getting ever nearer the edge, and in the process doing quite a bit of physical damage to himself.
He was an occasional social drinker, the first stage above complete abstention.
Funny thing is, you're listed on our books as a moderate social drinker.
For years, after law school, he'd been a light social drinker, nothing serious.
You used to be a social drinker-but of late you've been drinking frequently when you're alone.
June was emphatically not a science fiction reader, and Paul only a recreational one, like a social drinker: that last sentence was reasoning more sophisticated than expected for either of them.