The Indo-Iranian polytheists of Chitral and present-day Nuristan (erstwhile Kafiristan) seemed to have really hated Mohammedans in the 19th century. They would sacrifice to the Gods with a prayer to "Kill the Mussulmans" and considered killing Mohammedans their religious duty. 
In the 1800s, these Indo-Iranian "Kafir" polytheists of Afghanistan and Pakistan killed any Mohammedans who tried to enter their valleys and a young-man was expected to have killed a Mohammedan before he could marry. Lieutenant William Watts McNair of the Indian Surveyor Corps had recorded in 1883 that the Indo-Iranian polytheists of Kafiristan considered “slaying a Muslim” to be the most notable deed.
The head of the victim was put on a tall tree. 
This intense hatred of just Muslims seems to probably be a consequence of having to deal with repeated invasions of their homeland by different Islamic Empires in different centuries; Ghazni, Timur, Akbar all had attacked them unsuccessfully. They had beaten them back. The reason we say they specifically only hated Mohammedans was because they welcomed Sir George Scott Robertson because he was an English Christian. The Christians were seen as fellow non-Muslims and hence as “honorary Kaffirs” 
This dislike of only Muslims as being especially ritually impure seems to have continued to date in the modern-day Kalasha Indo-Aryan people of Chitral.
Muslims cannot join in any of the Kalasha-mun festivals but non-Muslims can. 
