My question is why do people act strict against other religions and why do they do that for is it because "they are jealous of them" or just to act cool in front of other people so other people can like them.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger as well as that of his family and all his companions.

A Muslim has to believe that Islam is the true religion and Allaah does not accept any other than Islam as a religion. Allaah says (interpretation of meaning): {And whoever seeks a religion other than Islam, it will never be accepted of him, and in the Hereafter he will be one of the losers.}[3:85], Allaah further says (interpretation of meaning): {Truly, the religion with Allaah is Islam.}[3:19] This religion (Islam) is the religion of all Prophets and Messengers from Aadam to our Prophet Muhammad . Indeed Islam is submitting oneself to Allaah, obeying Him and fulfilling His commandments and declaring oneself free from Shirk (associating partners to Allaah) and free from those who associate partners with Him. 

All the Prophets submitted themselves to the worship of Allaah Alone, obeying him and fulfilling His commandments, and all of them declared themselves free from Shirk (associating partners to Allaah) and free from those who associate partners with Him. 

Allaah says about Ibraaheem (interpretation of meaning): {Ibraaheem (Abraham) was neither a Jew nor a Christian, but he was a true Muslim Haneefan (to worship none but Allaah alone) and he was not of Al-Mushrikeen (idolaters, polytheists, disbelievers, pagans…)}[3:67].

Allaah says about Moosaa (Moses) (interpretation of meaning): {And Moses said, “O my people, if you have believed in Allaah, then rely upon Him, if you should be Muslims [i.e. submitting to Him]}[10:84].

Allaah also says about Nooah (Noah) (interpretation of meaning): {And if you turn away [from my advice] - then no payments have I asked of you. My reward is only from Allaah, and I have been commanded to be of the Muslims [i.e. those who submit to Allaah]}[10:72].

And Allaah says about Ya'qoob (Jacob) (interpretation of meaning): {Or were you witnesses when death approached Jacob, when he said to his sons, “What will you worship after me?” They said, “We will worship your God and the God of your fathers, Abraham and Ishmael and Isaac-one God. And we are Muslims [in submission] to Him.}[2:133].

Allaah also says about Yoosuf (Josef) (interpretation of meaning): {Cause me to die as a Muslim and join me with the righteous}[12:101] Allaah further says about the Queen of Sheba (interpretation of meaning): {…and I submit (in Islam) with Solomon to Allaah, Lord of the worlds}[27: 44].

Therefore, it becomes clear that the religion of all the Prophets, may Allaah exalt their mention, is one, which is Islam. However, their Sharee'ah (Jurisprudence) were not the same regarding the permissible and forbidden matters, and acts of worship. That's why the Prophet said: "I have the best claim to ‘Essaa (Jesus) son of Mary in this world and in the Hereafter; the prophets had different mothers but their religion is the same. [Al-Bukhari]

Thus, a person believing that the religion of Islam is the true religion and all other religions are false, must not be described as a strict person, and whoever qualifies him as such could apostate from Islam. Despite the fact that this is the true faith, this does not mean that believers in other religions should be dealt with harshly, because among the people of other religions, there are those who are belligerent and those who are not. Allaah says about the non-belligerent (interpretation of meaning): {Allaah does not forbid you to deal justly and kindly with those who fought not against you on account of religion and did not drive you out of your homes. Verily, Allaah loves those who deal with equity.}[60:8]. As regards those who are belligerent, Allaah says (interpretation of meaning): {Allaah only forbids you from those who fight you because of religion and expel you from your homes and aid in your expulsion — [forbids] that you make allies of them. And whoever makes allies of them, then it is those who are the wrongdoers.}[60:9]. So a non-belligerent is treated kindly and a belligerent is treated harshly. But it is forbidden for us to love both of them or take them as allies or friends, as they both disbelieve in Allaah and His Prophets, so how could a Muslim love them and be an ally to them?

Finally, we should note that after Allaah has revealed Islam-with today's meaning - it is not permissible for anyone to abide by any other religion, either in belief or in action; as the previous verse indicates: {And whoever seeks a religion other than Islam…}[3:85].

Allaah knows best.