You might not be able to tell from the brutal jokes the Comedy Central roasts have included over the years, but there were actually subjects that the people being roasted felt were off-limits. William Shatner reportedly prohibited anyone from making jokes about his late wife during his 2006 roast. And Charlie Sheen, who’d initially said he was cool with anything people wanted to throw at him, later requested that a remark about his mother be cut from his 2011 roast. For Joan Rivers, the only thing she asked people to avoid was making fun of her daughter, Melissa. However, Greg Giraldo, who was on the dais the night Rivers was roasted back in 2009, had other ideas. When a joke about Melissa came up in the writer’s room, Giraldo couldn’t resist using it, especially considering that Melissa was famous herself and wasn’t a child. After taking the stage that evening, Giraldo hit the crowd with the following: “Joan and Michael Jackson had a lot in common.…