Haha, I am told that I always say not too bad when I meet someone. Again, we use many of these statements when we meet someone we know. I think many Brits use such phrases in order not to say or avoid saying their true feelings.

When someone asks how you're doing in the morning, in all honesty they are just asking out of politeness. 'How are you?' is principally a greeting in English rather than asking how someone is really feeling. Hence we just say 'not too bad', 'I'm alright', 'I'm doing OK', or some other short response. Don't be misled by the use of 'not' in 'not too bad'. 'Not too bad' is a good response. Saying 'I'm fine' is a perfectly acceptable response too when someone asks. I definitely recognise what you have said. 'Not too bad' is my standard response. I guess it is cultural. As a general rule British people do not like to be too enthusiastic or 'over the top' about the state of things. If you are just having a normal day and everything is OK, then I don't know, saying 'I'm fine' or 'I'm good' sounds a bit too positive lol. It's a weird thing to describe. We differ to Americans in that on the whole we're a bit more pessimistic in the UK.

You're right, Elena, it probably is a cultural thing! Of course, these conversations are just standard greetings, and we are not really talking about our state of health. When we are saying hello to friends, neighbours and colleagues, 'not too bad' often means exactly the same as 'fine'. It's just a polite response. If you're interested in learning why British people behave as they do, I'd recommend a book called 'Watching the English' by anthropologist Kate Fox. She observes that British people respond to many situations by making comments along the lines of 'Well, I can't complain'. In this respect, we are very different from the more positive and optimistic Americans, for example. The 'not too bad' response is a typical example of this very British attitude.