I can't stand my uncle's jokes!!!?

They're not rude or prejudice or anything like that. They're slightly persecutory, but intended to be in good fun. Some of these jokes would go along the lines of "hey, you're a good for nothing blah blah blah" in a surly tone, as if telling you off for something. I'm a very serious person, and spend most of my time with people of similar personality types as me. When someone makes a joke such as this one, I get caught completely off guard, and don't know where to put myself. I take what they say literally. Once I went to my aunt and uncle's place, and my uncle came at me with one of these 'jokes', and my anxiety and blood pressure went through the roof, to the point where I nearly burst into tears. I felt so horible in making him angry that I just wanted to pass out. I seriously thought I did something that upset him. (There are a lot of things that young people do that elderly people don't approve of). But I soon realized that he was actually joking, and forced myself to laugh. His facial expression and tone of voice remained the same, and I was back to thinking he was really angry. He then realized that he had 'got me', like he always does, and laughed at me. I know he's well intentioned, making people laugh, but I just wish he wouldn't do this. I'm a highly strung person, and always concerned about what people think of me. I sometimes don't even understand sarcasm. How do I know when my uncle is joking? And how do I ask him to stop cracking these distasteful jokes, without coming across as a 'nark' (his words, lol) or hurting his feelings?