Basically, a half and half drink (half vodka, rum, etc. and half mixer), that is made only by ballparking amounts with no exact measurements. Typically made by the college crowd who can only afford lower tier alcohol, it is designed to get you fucked up as fast as possible so you only taste the shitty alcohol for as little time as possible. The more drunk you get the better they are. Another great part about the Flying Castelli is that when drunk party girls ask you what you're making, and you have no fucking clue how to make anything, you just tell them you're making a Flying Castelli. They are instantly impressed and think it's some exotic drink, when in all actuality you are full of shit and just gained some poon points with some drunk girls.
"Man, I am so fucked. Pour me another Flying Castelli."
"Chris had one too many Flying Castelli's and thought he could fly. He jumped off the couch and broke the table."
Drunk Girl: What are you pouring?
You: Well miss, it's a Flying Castelli.
Drunk Girl: Oh my god! Are you a bartender? Did you go to bartending school? That's so hot!
You: Yeah. Something like that.
*Poon Points acquired*