A few things come to mind:

1) This guy has no clue about coffee. He doesn't understand that dozens of people had to work to bring him his morning cup, from the farmers to the processors to the shippers to the roaster to you. Ignore his ignorance, even when it is tinged with anger; he obviously has other problems in his life than the fact that people tip baristi.

2) Are you a barista who is worthy of tips? Do you pull great shots? Do you know about coffee's flavors, how to serve it, where it was grown, etc.? In other words, are you doing things other than "pushing buttons"? In my opinion, most "baristas" aren't; they're "fast-food servers/cashiers". Make yourself worthy of the tip by growing and learning (IMO, your wage should reflect this, too; $7-8/hour is a fucking insult).

3) If he was rude to you, refuse him service next time. Let him go somewhere else. Let him realize that YOU are in control of his morning cup. Demand respect, as you are a living, breathing, thinking human being; if he doesn't see that, kick him the fuck out.

I hate to be bitchy, but clearly this guy decided that you weren't doing your job correctly. That doesn't mean you weren't, but he obviously expected something that you didn't provide.
I am not justifying the behavior at all, as I don't think it's acceptable for a human being to speak to another human being like that. But if you believe in customer service above all else, then you have to know there was a customer service failure here. (Does it matter that he only had coffee? Are regular coffee customers less important than latte drinkers?)

But, even if he was having some sort of personal issue (customer service or otherwise) I think it's ridiculous that he treated you in such a manner. And that he made such a sweeping general statement because he somehow felt personally slighted.

How would I respond? Obviously there are nuances to every situation, so you can't react exactly the same to every one, in this case I probably would have either told him politely that it's not required, I may have said "I'm sorry, is there something else I can do for you?" or I may have made a snippy remark about how only grateful people do.

I would never, EVER refuse service to him the next time he came in, however. In fact, the next time he came in, I would probably be more polite than I usually am. I probably would try to kill him with kindness, and even moreso if he were angry the next time he came. Generally, the ruder a customer is, the sweeter I am, because I will either win them over, or piss them off because they can't be pissed off at me, no matter how much they want to be.

But that's just my 2 cents (and you probably aren't worried about it any more since it's been over a year :)

next time, give him decaf :)

people are selfish tightwads