There are two situations:
1. when you have done something all by yourself, for example you did invent some new gadget all by yourself and somebody asks you, who just did that!!!!! than you say it was all me.
2. Second one are actually kind of people, who want to project themselves everywhere they go and if you agree with them on anything they will be happy but would always argue if you disagree. In this situation we don't that, "its all me" here its describing a personality. Cheers:)))