Alan you've been given some good Kennel advice here and I am glad you came here first to discuss and seek advice.
This is my opinion on the situation, and I will give you both sides of me, I to work in a corporate environment as well. I almost live a double life as the way I carry at work is not how I am after hours. You have to play their game.
In working hours
(a) You either reach out to your HR department and report if officially so they have something on record, or at least to a manager that you can completely trust and tell them the situation in strict confidence. No point telling a colleague or friend because I'm sure they will tell you what you've already been told here on the Kennel.
(b) Have a word with him in a political manner (remember you're in a corporate environment things work differently in a office than on the streets) so you have to be smart about it and play the game.
Stand up to him, approach him and ask him "Mate, I want ask you something about something that I have heard blah blah blah" but say it in a way, where you're standing your ground, strong but not to the point where you're threating him if you know what I mean. That way he knows that you don't take shit and if it was on the streets you'd break his face.
Other side of me
(a) Investigate/Recon - Find out if he is on facebook, Instagram, LinkedIn, Google (social media) find out anything you can about him, what car he drives, find out if he has mutual friends, find out where he lives, places he has checked in, places/areas he has tagged his pictures in, from that you can almost tell what area he is from or where he likes to go maybe clubs, bars etc... You might see him a regular at a particular bar or club on Friday or Saturday nights, based on the tagged pictures.
(b) Once you find all that info, either go with your mates to those areas and do what ASSASSIN suggested. If it was me and IF I was to choose this path I'd make sure he will never say the word that has any association with Homosexuals again!
There are so many things you can do.
But if you're a smart man and I'm guessing you're born in 79 do what you think is right without getting into trouble with the law honestly going to jail, court, a conviction towards your name isn't worth your money and time for a piece of shit like him, trust me on that.
Fagget ****!!