This. Here a few suggestions to start with:
Cheerily walk past him in the mornings in your riding gear and tell him how nice you ride was.
Tell him how many cars you overtook on the way in.
How much you prefer cycling in the sunshine to being stuck in traffic.
Is he fat? Point this out.
Tell him how much weight you’ve lost from commuting on a bike.
Tell him how much money you save on fuel by cycling instead.
Point out that on average cyclist earn more money and live longer then non cyclists.
Unless you’re 12 years old then I would bother doing any of the above. Just be normal, if he starts a conversation about hating cyclists then challenge him on his reason. But just be a grown up about it.
Tell him what you think of him, remind him he’s useless to humanity and never speak to him again.
So like have a tantrum and go in the huff? Yep that’ll teach him that cyclists are just normal folk.