Thing about Malcolm Tucker that you need to understand is that he’s not a dick…well, okay, he is a dick, but MOST of the reason he’s such a dick to people is that he has, just, an AMAZINGLY low threshold for idiocy, and basically everyone around him is a moron. He’s basically trying to nail jello to trees every fucking day by trying to create competency where there is none, and that makes him understandably cranky.
Sam is not incompetent, and therefor is saved from his wrath.
Also, she gets him people to shout at, so of course he likes her.