Snape doesn't know when to quit. I can see him dumping on Harry in Potions Class in front of Malfoy because Malfoy is a snitch. If Snape wants to protect his cover working for the Order (he used to be a Death Eater), then his nasty attitude makes sense. But come on, Snape you're a big boy now. Whatever you suffered because of James Potter is ancient history. Get over it!