The joke SHOULD have been believeing you can catch the gay.
Lets take the other anon's argument. and merge it with your counter. If you're not gay, you're not gay. if you dont WANT to be gay, then you wont be gay.
Catching the gay implies you are becoming gay against your "will", which means it came naturally.
Therefore, you already HAD teh ghey from the very beginning if you ever think you "caught" it.