ok - so I'm a teacher. I'm appalled.
But look, stuff that happened a few weeks ago is a problem... Were there witnesses? why did you wait so long etc etc... And look I bet there are good reasons, kid was scared, didn't want to talk about it... All fair enough, but the school could get defensive and argue that the delay is for another more sinister reason...
My thoughts... Have a chat to your son. Make sure he is doing the right thing... But tell him a bit about bullying. But be really careful here PLEASE.... My thought, tell him to ignore it. Tell him to be on his best behavour... Tell him to aviod being alone with the teacher... More importantly, tell him that if such language is used again, he should politely stand up and say something like "Mr XXXX you have just said XXXX. I am now going to the prinicipal. I would like the other students to note that they witnessed you bullying me". Then he walks to the prinicipal and politey waits for the principal, or deputy to speak to him...
So that is one thought. Another thought, contact the school, ask to speak to the principal, or write a letter directly to the principal. I reckon a letter is a good idea... If you speak to someone like a head teacher, or year advisor, things can get swept under the carpet. By putting it in writing, you're putting the school on notice that they really need to act.
I have attached a link to the nsw det complaints policy (I'm assuming it is a public school).
Complaints Handling Policy | Policy library
If you write a draft of a letter to principal, without names etc AND DO NOT MENTION THE NAME OF THE SCHOOL, OR EVEN THE GEOGRAPHIC REGION. i will give you my thoughts on the letter.
Look if the teacher has done this to your son, he may well have done it to others, there could be other records and as such the school really should act to either counsel the teacher, or look at other disciplinary options.
BUT make sure you're very clear on the details... Like I said, I'm a high school teacher. There are lots of things I say in a day that when taken out of context sound pretty bad... So for example, I had a complaint about showing a racist cartoon... I was teaching history and the cartoon was about the White Australia Policy. It was a stupid complaint, but I still had to deal with it... that said, calling a kid 'a poof' is something that I can't find a context that I reckon can justify that sort of terminology.
One more thing. Dont be anonymous, teacher will work out who is complaining, and teaching your kid to stand up for himself is something to be proud of