@Christmasobsessed
What do you mean?
If this is with regard to 'You clearly have bigger issues':
Your partner is regularly disrespecting your son in a way that may well cause him psychological issues (such as low self esteem) for the rest of his life. Being called names by a primary caregiver can really screw up a child. They don't always show signs of being bothered at the time, because they don't realise or understand the implications, but it erodes their self esteem when, for example, they get older and realise that nobody else was called names by their Dad; the question then for them is 'Why was I different? Why was I the one who got picked on by my Dad? What did I do wrong?' The damage can last a lifetime, and have an effect on their primary relationships (with their own partners and children), on going. That's the initial problem. It's not just about 'I don't like that word, stop saying it'. It's the ethos behind thinking it's ok to say derogatory things to a child. Your son does not have a good father
The other problem is that he tells you to shut up. In this context or any. This is blatant disregard of your feelings. Why doesn't he care that he's upsetting you? Why doesn't he think your opinion is valid in the upbringing of your own son? Your partner does not respect you
The only solution here is to stand up for your son, at the time, against your partner, which will bolster your son's self esteem. If your partner tells you to shut up, this will start to demonstrate to your son that 'Dad is horrible to mum', which will show him that the horribleness isn't due to his own failings. But that situation cannot continue for any length of time. It is damaging in itself. Privately tell your partner that if he keeps doing it, you will leave. And then follow through. Your son will have a much better chance of obtaining a good level of self respect if he can say 'My dad used to call me names, so my mum and I left him', than if he ends up saying 'My dad called me names all through my childhood. My mum asked him to stop but he told her to shut up, so she did. Every time.'