Muhammad: The Dead Poets' Society
Even while Muhammad lived in Mecca revealing the "peace and love" Islam (not that there was a lot of it) that Allah later replaced with the "obey or die" Islam, he gave many, many warnings of what was to come to disbelievers and especially critics. I'm pretty sure this still applies to people like me and you, whether we can rhyme in ancient Arabic or not.
Woe, on that day, to those who have rejected God's revelations and those who have rejected the Day of Judgment. No one rejects it except the sinful transgressors who, when listening to Our revelations, say, "These are only ancient legends". They will never have faith. In fact, their hearts are stained from their deeds. On the Day of Judgment, they will certainly be barred from the mercy of their Lord. They will suffer the heat of fire [hell] and who will be told, "This is what you had called a lie". - Quran (83:10-17)
Al-Nadr bin al-Harith was a poet and particular gadfly of Muhammad's
in Mecca following him around and mocking him at his public recitations.
He was captured at the battle of Badr and he was one of the only two Meccans beheaded that day as ransom was more important than revenge to the Muslims at that time.
Uqba bin Abu Muayt was the other poet who mocked Muhammad that was captured and executed that day. "But who will look after my children, O Muhammad?" Uqba called out.
The prophet Muhammad (peace be upon him) replied "Hell!"
Asma bint Marwan was a Medinan poetess who wrote poems tearing new arseholes for the men of Medina for letting Muhammad and his crew take over.
Muhammad was down at the mosque and called out, "Who will rid me of Marwan's daughter?" A member of her husband's tribe volunteered and crept into her house that night and "gently" removed her baby daughter
who was sleeping at her breast and then hacked her to death. She certainly had the "men" of her tribe sussed out. They rolled over and assumed the position for the Muslims.
You didn't even have to be a poet, it was enough to disparage Muhammad to get the chop. Ali ibn AbuTalib the fourth caliph, and the son-in-law of Muhammad remembered what Muhammad decreed about this "justified" murder:
A Jewess used to abuse the Prophet (pbuh) and disparage him. A man strangled her till she died. The Apostle of Allah (pbuh) declared that no recompense was payable for her blood. - Sunan Abu-Dawud, Book 38, Number 4349:
Actually though it was not a crime to kill any opponent of Muhammad, it was not a crime to kill any opponent of Islam. These murderers were heroes and would possibly get more than the usual quota of virgins in heaven.
There are many more similar stories but considering how many innocent people who'd never heard of Muhammad were killed by Muslims in later years these are not really important except to shine a light on what sort of man Muhammad was. Not one to let go of a grudge and dangerous to ridicule.
Muhammad claimed the poetry of his "revelations" was so excellent, so incomparable, so miraculous even that only God could have created them and that no-one could possibly create anything similar. The history written by Muslims claims no Meccan poet could meet this challenge but as those real connoisseurs of 8th century Arabic poetry - the sophisticated, cultured classes of Mecca - continued to spurn Muhammad's religion until he gained military power over them we can see that the "poetry" of the Quran was not impressive. Muslims give many excuses why Meccans rejected Muhammad but the awfulness of the Quran is reason enough for me.
And if you (Arab pagans, Jews, and Christians) are in doubt concerning that which We have sent down (i.e. the Quran) to Our slave (Muhammad Peace be upon him ), then produce a Surah (chapter) of the like thereof and call your witnesses (supporters and helpers) besides Allah, if you are truthful. But if you do it not, and you can never do it, then fear the Fire (Hell) whose fuel is men and stones, prepared for the disbelievers. - Quran (2:23-24)
A list of the killing of individuals ordered by Muhammad is available at WikiIslam.
A much fuller article about Muhammad and his revenge on poets of his time is available here.