I've noticed that normally when anyone offers Columbo an alcoholic drink he either refuses or he accepts the drink but either only takes a small sip or doesn't drink any of it at all before saying he has to run along or whatever. Something I've noticed in quite a few episodes so it must be intentional. I guess that he doesn't drink too much while on duty as he wants to keep a clear head. Of course there are exceptions too where he does drink more like food and wine related episodes such as "Any Old Port in a Storm" and "Murder Under Glass".

Don't forget THE CONSPIRATORS where Columbo I think does legit drink quite a bit with the Irish murderer.