This doesn't seem to match the Russian sentence. For one, (excuse the following) "пидорас" = "faggot" in English, and I'm not fluent in Russian but it seems to be saying something like, "If you only do it once, you're not a faggot"?

You're aware of idiomatic translation rather than copying everything word-for-word, right? :)

Knowyourmeme said:
“It’s not gay if…” is a phrasal template in which the author claims that homosexual sex is heterosexual, or otherwise doesn’t count as gay under certain conditions."
Basically, the phrase is used to say it doesn't count. Same with the Russian one, although a different reason for that is given. An idiom for an idiom. A literal translation would be stilted, as it often the case with catchphrases.
Of course, both phrases can be used figuratively to refer to something other than homosexual intercourse as well. :3

Yes but I don't think these idioms are equivalent. The English idiom is nonsensical and tongue-in-cheek; the Russian makes perfect sense if you replace the slur with something less offensive. Most healthy people experiment with their sexuality once or twice, and often it's how they figure out what types of people they are comfortable with.

Even in English we say similar things to the Russian phrase, and those things are not considered to be nonsensical.

Ah, are you one of those people who think they have discovered The Truth and look down upon anyone who doesn't bow to it? :{

The English sentence doesn't seem nonsensical at all, like a gibberish phrase would. It's just a silly thing to say that's not literally true and doesn't get taken seriously because of that.
The Russian would be quite similar in that regard, except it's somewhat more rude. But not as much as you probably think, given that the word has been progressively shifting from a specific slur towards homosexuals to a general label for an 'asshole'. Slurs losing their bite and slowly growing inoffensive is much better than innocent words becoming slurs because some people just aren't happy with them, if you ask me.

Words that marginalized people consider slurs can only be perfectly innocent from the eyes of someone who believes they have stumbled upon "the Truth" and looks down upon anyone who doesn't bow to it.

Me, I'm just going with what any medical website about sexual health would tell you.

It was me who added this as a translation to the Russian sentence. I don't mind them being unlinked.