Scenario 1; "Sorry, but I'm not comfortable enough with you to consider dating."
Scenario 2; "Sorry, I don't know you well enough to consider something like dating."
Scenario 3; "That's really sweet of you, but I'm not looking for a relationship with now."
Scenario 4; "I think of you more as a friend."
Scenario 5; "I think you're a great person, but I'm not ready for a relationship with anyone at this time in my life."
Scenario 6; "Hey, I think you're a cool person, but don't use your birthday as an excuse to get with me."
Scenario 7; "uhm, no."
:pDon't be intimidated by the fact that he is using his birthday as support to his question. I know he's your friend and everything, but that's called guilt tripping and you don't do that to people that you consider your friend, or someone that you have any respect for. Kind of a sleaze ball move.
If he used it in a joking manner, then don't worry, he'll still be your friend if you say no. Just get him a gift that you know he'll like, he'll get over it :)