I am afraid to tell you how old deranged/pornographic/quite possibly ingenious Bronx rapper Kool Keith, he of the myriad aliases and wildly erratic and thoroughly entertaining live shows, actually is — it will only depress you. And him. And yet the announcement of an honest-to-god Kool Keith Birthday Bash is a wonderful thing, in that it will either be absolutely terrible or improbably transcendent. One or the other. Can’t say that about many artists these days. An East Village Radio/Brooklyn Bodega co-production, it goes down Thursday night at Southpaw in Brooklyn, starring Keith’s old crew the Ultramagnetic MCs, Jesse West, Large Professor, and OG Chino; “Bring flowers,” you are advised. The flier is below. This is gonna be ludicrous.