Because like most people with ‘cluster B’ personality issues, he’s very thin skinned, requires constant ‘narcissistic supply’ from everybody, and can’t rise above any insults or slights, real or imagined. It made him look bad enough when he was having his ongoing childish spats with Rosie O’Donnell, letting her get under his skin so easily before he became president; now it’s totally inappropriate. It’s been obvious ever since he took office that he’s not cut out for the job. Even George Bush, Jr. wasn’t as easily baited as this guy. He’s too emotionally labile, the part of his brain which has to do with executive functions such as inhibition of destructive and self-destructive impulses, among other things, is obviously damaged. It’s actually a bit of a national security risk that he is so sensitive and quick on the emotional trigger like some 3rd world dictator. Makes us vulnerable. We have to stop letting cognitively impaired people with low ‘emotional IQs’ run this country.