Have A Couple Meaning

(idiomatic) To drink enough alcohol to be slightly drunk

Example: 1992 Wesley Gibson, Shelter, Harmony Books, p144
  He's kind of funny and likes to play the guitar when he's had a couple.
2005 Fay Freimuth, A Multitude of Mercies, iUniverse, p155
  It's like he sees me as a woman once he's had a couple.
2008 Andrew Fusek Peters & Polly Peters, The Rock from the Sky, Evans Brothers, p41
  For even the puniest, wouldn’t know a muscle if it shook his hand at a party and said ‘Hello, I’m Mister Bicep,’ foul-mouthed, inconsiderate, insensitive, ‘isn’t a feeling what you do with your hands?’ oaf– once he's had a couple (and he is dreaming of coupling) – voila!