Hmmmm... It's difficult to say what is meant by that phrase, as it seems to be a conflation of more than one phrase. In American English, "in your face" (more often: "in yo' face") is an expression of derision of another person; it is demeaning, especially used when one has just beaten another at something (quite often in sports competition). I know that in Jamaican English, and consequently in the British English of a certain ilk, "big up" has an antithetical meaning to this: it is an expression of respect or acclaim, often used by D.J.'s in clubs to "pump up" the crowd. Actually, the language that you quote has the typical aspect of a promotional flyer. I suspect that "a big up-in-your-face event" might come from a promotional flyer for a party, written by someone who either doesn't know proper use of these phrases or doesn't care, and just wanted to say something (whether it made sense or not being immaterial) that would make the event he is promoting seem "oh so exciting" (at least for the uneducated).