lately it seems like he's drunk all the time just so he gets some lines.
It's clearly psychological, considering simply taking a sip of a beverage is enough to get his courage up in several instances.
(Not that I'm saying it could be anything but
In one episode where they took a train ride (and met Summer Glau) he drank an alcohol free beer and talked to the female Terminator without realizing he wasn't buzzed at all.. when they pointed it out he immediately shut down again.
Agreed though.. that particular gag is played out but for some reason they don't want to let it go. Ah well.. sometimes it still makes for a funny scene.