Booyakasha is a polite way of saying booya.
It comes from hebrew בְּבַקָּשָׁה (b'vakashá) which means "please" or "you're welcome" and from booya (see booya)
Sasha Baron Cohen probably invented it for his character Ali G.
This is a word very stupid people like to pretend exists because they have recently been using it in excess, however no one uses it so they just sound a little bit silly.
Prehaps and incorrect abbreviation of 'Boyakasha'
1) A very positive exclamation.
2) An expression used to denote superlative coolness.
3) A Web site that uses Ninja-like techniques and mutant powers to help people create and complete creative film projects.
1) "Boolaka! I just won the lottery!"
2) "Girlfriend, your new jeans are boolaka!" "The boolaka kids all eat lunch together, including the class president and the jocks."
3) See Boolaka.com for a complete explanation.