Ta-Nehisi Coates has a blog post up about Lupe Fiasco's anti-Obama rant with the headline, "My President is Whack." Though we hold Ta-Nehisi Coates in high esteem, we must interject here: no, My President Is Wack.
"Whack," or "Wack?" The answer is "wack." The word meaning "bad, messed up, stupid, boring, dumb, uninteresting, unenjoyable, or otherwise not good" is spelled "wack." The letter "H" is not involved. Some random grammar site declares, "The word meaning very bad or of dubious quality is wack, with no h." On "My Philosophy," KRS-ONE said "they all just wick-wick-wack." The plague of the world is wack MC's. There's even a shitty Youtube rap video entitled "My President Is Wack," featuring the comment "your flos are hella wack."
The most important thing to remember about all of the evidence above is that none of it proves anything, because "wack" is a slang word and slang words are inherently flexible and ever-changing and and slang is whatever we make it. There is no appeal to authority that can settle this argument once and for all. You can drag in a thousand old school rappers to say it's spelled one way, and a thousand old school rappers to say it's spelled the other way, and it still will not be settled, because, look, it's spoken slang, so when you ask how it's spelled, you're just asking someone to make up a spelling on the spot. The "real" spelling and usage of slang words is—like sports, or who makes the best hot sauce—a perfect thing to argue about, because there is no answer, except the answer mutually agreed upon by the people having the argument.
The only way to settle this argument is this: it's wack. It's not "whack." That shit looks ridiculous.