When he realises he likes you (Friendly way):

9th Doctor:
He liked you from the moment he saw you pulling a kid behind you when the boy with the mask appeared. He knew you would always put other before yourself.

10th Doctor:
He liked you from the moment you said something very clever. It wasn't one of the things you knew a lot about but you approached it from a new angle. He was just amazed by how creative you were.

11th Doctor:
He liked you from the moment you stood up to your 'family'. He knew you saw the Silurian's as your family so when you stopped them from harming him he was very surprised. You didn't even knew who he was!!

Rory:
He liked you from the moment Amy told him about you. She was always talking about the Raggedy Doctor but when she started talking about his Chatty Nurse listening to Amy became interesting. As Amy's obsession with the Doctor grew his one for you did too.

Mickey:
He liked you from the moment he noticed that you were actually listening to him. It was a new experience for him because he was used to people ignoring him but you were actually listening!! Even rose hadn't managed that.