"Drunk squirrel" is not a species of squirrel but a reference to squirrels that have eaten fermented pumpkins or berries. Humorous videos and stories of "drunk" squirrels are widespread on the web and are a source of amusement for many.
Squirrels don't get drunk on purpose, though eating fermented foods is a common occurrence. There are many animal species that become intoxicated after eating a fermented source of food. While it's amusing to see animals in a state of inebriation, there's no evidence to show that any animal species actively seeks out intoxicating foods with the intention of getting "drunk."