Explain this cartoon please

Otherwise known as The Drunk Scotsman.

NB Nae/Nay might mean “no” in parts of England, but it isn’t used that way in Scotland. In Scotland it’s the equivalent of “not”. For example “He’s nae comin oot the day” or “I huvnae got a clue” (to complicate things, you probably wouldn’t hear both of those pronunciations in the same part of Scotland).