Justin Bieber finally got his just deserts this weekend when he came down with a very public, very gross case of Stage 5 Bieber Fever in front of thousands of adoring Beliebers. Bieber had just taken the stage when the Bieber Fever manifested itself in the form of wave of nausea and, eventually, the classic sign of Stage 5 Bieber Fever: the dreaded Bieber Barf. So it goes: Bieber reaps that which he sows. To his credit, his explanatory tweet was actually pretty funny …