Who named Christians?

The Qur'an and hadith specifically call followers of Muhammad to label themselves Muslim and their religion Islam.  They criticize Christians on the basis that Christ never directed them to call themselves anything.  But anything or group of things needs some sort of name with which to distinguish itself from others that are not part of the group. A simple descriptive is sufficient, if it conveys a correct and universally understood appellation:

Christ followers = Christian.
Native of Germany = German
Guard of a person = Guardian
Resident of Rome = Roman
Someone from Africa = African
Associated with Arabia = Arabian
Someone from Mesopotamia - Mesopotamian.

English. It's not that difficult. Muslims should learn to speak it sometime, and quit twisting themselves around stupid little word games that mean nothing.

I don't understand the source of this imaginary mandate for God to label His children.  Is there some mental fixation Muslims have - that a follower of Yeshua needs to be told how he should refer to himself?