Why do cats put their bum (butt) in your face?

Well to be honest mine don't do that! Maybe we just think that cats put their bum in our face because we as humans are sensitive to what we consider rude behavior but which the cat considers acceptable and normal.

In other words in the normal course of events our cat will present his or her bum to us and she will present her face to us etc. We are just overly sensitive to those times when our cat presents her bum to us and think there is some sort of weird reason for it.

Cats do put their bum in the air when you stroke them. The reason is on this page. That might be what people are talking about. There is nothing in the books about cats putting them bum in your face other than as described on the linked page above.

There is one other possibility. Cats like to scent exchange. They like to deposit their scent on us as it makes them feel more secure. Scent glands are situated around the body including towards the tail. If a cat rubs against you with his or her rear area while at the same time being at around head height she is liable to present to you her bottom. That might be the reason why cats put their bum in your face.