what reasons can make a guy turns gay?

Your friend has no idea what he is talking about.

Nothing 'makes a guy turn gay' - up to and including being raped by a man (you do seem to be somewhat fixated on it though - which says a lot more about you than it does about anyone else).

A guy is either attracted to men, or he is not.  If he is, then he may be gay, or he may be bi.  Nobody 'turned me straight', and I didn't 'choose' to be straight, I'm just attracted to women, and not to men.

Your protestations against being labeled a 'troll' are weak, at best.

Lunacy in the crowd.

Maybe when someone starts speaking this sort of stuff, you should ask your self, just where did he get his education on this subject from??

You can seer the first serious flaw to his rant in the line that says "in my country"

Humans are the same in any country, he cant say that and in doing so is suggesting in other lands its different.

Personally if I knew a guy and he rolled that one out to me I would read into that, he is saying he wants me in his bed.

I would not argue with him, I would just ask what university did he attend where he studied homosexuality and if he did not where did he go to learn all this.

I'm tempted to troll this by saying there is a hormone in the aggressor's semen that turns the victim gay.

But to be honest, nobody "turns" gay.  

If you are not attracted to someone of the same sex, someone receiving anal sex forcibly, is not going to make that person gay.  FYI, there are gays who have never experienced anal sex.  

No one who had even one class in Psychology would believe that nonsense. Liking the sensation of having your prostate stimulated does not mean you're gay, just that you're male.

I call bullsh!t.  Either you are lying or your friend is lying.  The psychological community never says anything as ludicrous as homosexuality starting from rape sodomy.  That is an antiquated myth from probably the 1950s.  Real, actual psychologists know that homosexuality is a natural inborn trait that is hard wired into the brain from before birth and is never a result of any life experience.  There is no chance in hell that your friend "graduated from psychology" with a notion like that.  Where did he go to school, the University of Making Sh!t Up?  I for one have had sex with a male friend several times and enjoyed it greatly, and I am no closer to being gay or even bisexual than I was before it started.  I continue to feel zero attraction whatsoever to guys whether physically or romantically. 

There is are subheadings under the article "Young People Ask . . .Why Do I Have These Feelings?" on the jw.org website that might answer your question. 

In the last year of her television show, Oprah had on 250 men who had suffered sexual abuse as children.  Less than 2 % identified as gay.  The rest identified as straight.  As a psychologist (with a Ph.D.) and as a gay man, I can testify that this so-called friend of yours (unless of course you are making this up) is simply wrong, no matter what country s/he comes from.  Sexual abuse is no more a trigger for homosexuality than it is heterosexuality.  That particular potato was boiled away a long time ago. In fact, we no longer blame mothers, fathers,, the environment or even climate change for "making a person gay". 

Rape does not make you gay. It hurts.  

But other cultural and environmental factors like childhood sexual abuse can play a role. They have been studied. 

Homosexual orientation is caused by complex interplay of biological and cultural influences.