There are several theories about the origin of this phrase as in meaning a strong drink.
- Some have said that it comes from the West African word "kaketal" which means scorpion. Obviously, it would be the sting that the drink gives you which would lead to this conclusion. (A plausible explanation.)
- Some have said that drinks were once stirred with rooster tails, and this is where it came from. (That's pretty silly, if you ask me.)
- Others have said it has to do with Aztec princesses named "Xoctil." (Not sure how that would apply here.)
- The leading contender for the correct theory, it seems to me, is the one Webbie vaguely alludes to down there. Show horses would have their tails bobbed, which would make them look all dapper and jaunty. Thus, they were called "cocktailed" horses.
So, you could take it either of two ways: The kick of the drink would be enough to cock your tail. Or, the effects of the drink would make you all dapper and jaunty.