"I'm alright"

I have a friend who doesn't understand why I say this when I do. Actually, neither can I. But I say 'I'm alright' as a reply to questions quite often. Examples are:

Friend: "Laura, would like a cup of tea?"
Me: "I'm alright."

Friend: "This programme is a bit boring. Would you like to watch something else on TV?"
Laura: "I'm alright. I'm studying anyway."

Friend: "Would you like to stay for dinner?"
Me: "I'm alright, thanks. I'd better get home and study."

I'm alright?! How is that synonymous with 'yes' or 'no'? I use it to mean 'no' but why? Why is telling someone what your mood is like the same as saying 'no, thank you'? The friend who gets annoyed always replies with, "Yes, I know you're alright. But would you like a cup of tea?" He says that unless I'm really crying or have mentioned that I'm not feeling good for any reason, he can presume that I'm alright. But that's not the conversation he was having. He's asking me if I want something.

But I can't help it. It just comes out when I'm answering a question. 'I'm alright,' I say, as if it's an answer. I guess it means, 'I'm alright without it.' That's still not satisfactory because lots of things I'm 'alright' without but I still want them. I'm 'alright' without the cup of tea, no big disaster is going to happen, but that doesn't mean I don't want one. So no, it doesn't really make a lot of sense, no.

I definitely used to say 'I'm good' to mean the same thing. I remember being on a driving lesson and saying it. Driving instructor said something about lessons next week, was I going to book an extra one, or something, and I said, 'I'm good' to mean no.

It's like there are two different conversations going on. One person is saying, 'I'm asking you if you want something,' and you're saying, 'Let me tell you about my behaviour/mood.' It's quite rude really, just interrupting their conversation and starting a different one. Imagine if that's how all conversations went:

"Hi, how are you?" "I love cricket."

"Do you want to meet up for a coffee?" "Did you know my middle name is Louise?"

"I'll call you later." "I must remember to pick up the dry cleaning."

We wouldn't get very far in our interactions, would we? We'd all just be going on about random things whilst in the company of other people.

I must try using 'yes' and 'no' more often, I guess.

P.S. 16 days til first exam. Today's study topic is Formalities in Equity and Trusts Law.