What is the ruling of calling someone who is non Muslim "gay" without accusing him of adultery?

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.

If this person meant something acceptable by it and it was not meant to be an accusation of Faahishah (sexual immorality), then the one who said it is not subject to the Hadd (prescribed punishment) for slander. Otherwise, he is considered a slanderer.

Ibn Qudaamah wrote, “If one said to another, You, Looti, he is to be asked about his intention. If he said, I meant that you are from among the people of Loot (Lot), then nothing is required of him. But if he said, I meant that you commit the evil act of the people of Loot (i.e. Sodomy), then he is like one who has slanderously accused someone of Zina (fornication/adultery).” [Al-Mughni]

Allaah Knows best.