I mean that he had a terrible behaviour with non-muslim (kafir).
According to the Sira, the sacred biography of Mohammed, he was involved in over 65 acts of jihad, or as we say today, 65 acts of terror. And that was in a 9 year period.
Mohammed was violent in every way. He assassinated those who opposed him, enslaved thousands and sold them for money to wage jihad, he tortured men to death for money, tortured slaves to get information from them, created a policy of rape of Kafir women and on and on.
I don't know how true all that is, but from what i read he also had great charasteristics too.