For my mother.. she loves this part where Gilligan and this lady or maybe it was a different character than Gilligan... They're getting drunker and drunker and drinking champagne and laughing like weirdo's saying "more champagne" "yes yes thank you dear" Or something like this.. I MUST KNOW!!! THANK YOU!!:p

In 'The Matchmaker', from season 1, Gilligan and Mary Ann are invited to the Howells' hut in the hopes of bringing them together as a couple. They drink a lot of champagne toasts but I don't recall them laughing like weirdos, but that might be the episode you're after. :)

Doesn't ring a bell, I was thinking of the episode in which the two Russian comsmonauts land on the island and in the end all the men are having a toast with vodka but the castaways have secretly replaced one bottle of vodka with water.

Doesn't ring a bell, I was thinking of the episode in which the two Russian comsmonauts land on the island and in the end all the men are having a toast with vodka but the castaways have secretly replaced one bottle of vodka with water.
Let's try and think of all the eppies where they got boozed up :)

My Fair Gilligan. They didn't get boozed up but they did have a party and Gilligan threw a pie at Howell (and some of it hit Ginger which is something Bob Denver did on purpose.)

Nyet Nyet Not Yet, the eppy with the cosmonauts and the vodka. Do svidanya!

The Matchmaker.

Man With A Net. They brew alcoholic tea for Lord Beasley but they all get drunk instead because Beasley is British and he can hold his tea :)

Not alcohol, but Gilligan goes woozy in Topsy Turvy and acts like he's drunk.

Can't think of any more off the top of my head.