Anyone that is acting like a retard. It can also mean "let us celebrate," if said in a loud happy way.
George: Look at that halahishna!
Billy: Yeah! He has no idea how wrong that corn dog looks in his mouth.
Peter: I'm so pumped for this party! HALAHISHNA!!!
Billy: Yeah! He has no idea how wrong that corn dog looks in his mouth.
Peter: I'm so pumped for this party! HALAHISHNA!!!
by TheAmazingSchna_Of_Jonathan December 2, 2010