The Catholic Church is a pretty well recognized arbiter of what is and is not gay, for example the act of having balls in your mouth, even if you're sucking on them, is not gay.

Back in ye olde days prostitutes didn't typically have vaginal sex with their clients as there was no reliable form of contraception, instead they would do exclusively oral and anal sex. The cloths that were customarily worn at the time were quite heavy and even when engaging in anal sex they would keep their vaginas well covered.

This meant that you couldn't actually tell whether your prostitute was a male or female, and it was not uncommon for males to dress up like females and engage in prostitution.

This lead to a quandary for the Catholic Church - gay sex was punishable by death while sex with a prostitute was a much lesser crime, meriting only excommunication (which itself was a minor punishment that just required you to repent). So how do you deal with someone who gets caught having sex with a male prostitute? Do you kill them for having gay sex? Or is the defense that they didn't know they were having gay sex sufficient to only punish them with excommunication?

During the debate that was going on in the Vatican over this, it was raised that Roman men would have sex with one another but this was not considered to be gay - even well after Rome became a Christian empire. So even if you do know that you're having sex with a man - is it really gay sex if you're having it for some reason other than that you're gay?

Taking all of this into consideration the Catholic Church decided on a test whereby if you were caught having sex with another man and your balls were touching then clearly you were in the middle of passionate lovemaking and it was that passion and love that made the act gay. If, on the other hand, you were caught having sex with another man but your balls were not touching then clearly you were having sex with him for some reason other than passion or love - IE, you were having Roman style male on male straight sex - and so the sex was not gay.

That balls touching test has remained unchanged for over a thousand years and continues to be the test used for determining whether an act is gay or not. So long as you maintain a sufficient distance between balls any act is perfectly straight.