1. I'm not really into dancing.

2. I'm not interested in dancing at all.
3. I am not very interested in dancing.
4. In fact, I'm not interested in dancing.
(What does #1 mean, #2, #3 or #4?)

All of these mean the same thing. "Into" in sentence one is slang and it means "interested in" or "excited by".

All of the four statements express a lack of interest in dancing, but they differ slightly in their emphasis and tone.

1. "I'm not really into dancing" suggests a mild disinterest in dancing. It indicates that while the person may not actively pursue dancing, they may still occasionally participate or enjoy it to some extent.

2. "I'm not interested in dancing at all" explicitly indicates a complete lack of interest in dancing. This person has no desire to engage in any form of dancing.

3. "I am not very interested in dancing" conveys a less strong disinterest compared to statement #2. The person might not actively seek out opportunities to dance but may still be open to occasional participation or appreciation of dance.

4. "In fact, I'm not interested in dancing" implies a response to a previous statement or assumption, emphasizing that the person wants to make it clear that they have no interest in dancing whatsoever.