'I have a bone to pick with you' means 'I have reason to disagree or be annoyed with you.' and have been answered already. It would help if you would put the text of the whole paragraph or exchange. I was always told that the origin of "I have a bone to pick with you" comes from Old Hebrew. When God decided to make Eve in order to give Adam's right arm a rest, he warned him that he was going to have to lose a bit of genetic material and ossified tissue - it is quite possible that after God announced this, Adam reminded him that he had a bone to pick (to discard). hence the expression of somebody who has waited for an opportunity to point out something that they 'have a bone to pick'. Another origin may be that often people pick clean the flesh from bones of animals that they are eating. Animals contend over good marrow bones, so if by analogy two people are both having a go at a bone they could be said both picking at it. so to come together and strive could be said to be picking a bone together.

Bem, is right, and it usually implies a fairly long or detailed discussion. Like a dog chewing for a long time on a bone in order to pick all the meat off of it.

something that you say when you want to talk to someone about something they have done that has annoyed you