What it is.
Treating someone who is above you as your peer or lesser. For example, speaking about God as your buddy, your aunty as your sister, your teacher as your brother, a child speaking to an adult as if they were the same age, a young schmuck critiquing Don Carson, offering advice to those more experienced than you.
Why it is bad.
It is disrespectful. It is annoying. It makes me think you've got boundary issues and don't know where you stand in the world.
Oh no! I think I do that! How can I change?
Listen to what God says:
1Do not rebuke an older man harshly, but exhort him as if he were your father. Treat younger men as brothers, 2older women as mothers, and younger women as sisters, with absolute purity. (1 Tim 5)
Notice that we don't treat older people as brothers and sisters? That is presumptuous. We treat them as mothers or fathers. We keep some respectful distance. Honour them. But younger people, people below us in the pecking order, we elevate them to the position of brothers and sisters, thus lowering ourselves.
And with God?
It is hugely condescending for God to call himself our father. For us to be his children. But father is still a position of honour - more so 2000 years ago than now. Don't forget it.