Thanks for tagging me in this :) /u/spoderman, I'm sorry this is happening. I totally understand not wanting to cause trouble at work. Unfortunately, women are socialised very early to not make waves, no matter how inappropriate or bad the other person's behaviour is. And people are also socialised to expect that of women, so when we do stand up for ourselves, we're judged pretty harshly as arrogant or alienating.

However, nothing will change unless we do, and being condescended to like that grinds you down in a way that it's hard to describe. Most of the people doing it are not bad people, they've just been taught the same things we all have: that women are out of their depth in STEM areas and need help. Some psychologists have suggested that it's also a kind of peacocking behaviour - they're demonstrating their own knowledge to impress others. So shutting them down in a way that doesn't take that into account can lead to even the nice ones having their pride hurt.

The best way I found to do it was to, if at all possible, get other people to ask for my assistance in front of the person doing the over-explaining, which gave me a chance to demonstrate my knowledge. A friend of mine who is also a physicist, towards the end of her degree, had a group project which required extremely rigid reporting structure. When the group got together, one of the men focused on her and said, 'Now, this write-up can get complicated, so I can help you with that. There's a tool on the module website that formats most of the work, which I can go through with you, if you like?' One of the other guys was laughing, and said, 'er... [explainer], she wrote that tool. She's the adviser on this.'

You might not have a situation like that which you can exploit, but often being able to point to a specific achievement and bring it up in conversation can help remind them that you are capable and experienced. If not, a more forceful but still polite method is to interrupt the explanation and say, 'thanks, but I've got quite a bit of experience with this' and then redirect the conversation rather than leave that sting hanging. Ask a question or something but not one which puts you in the submissive voice.

There also seems to be some evidence coming up which suggests that women use the word 'just' as a way to defuse interactions where there is an imbalance of power. For example, 'I'm just checking to see if you've finished the coursework', 'I just wanted to ask if...', etc. It is a way of pacifying the other side, but it places the power in the conversation with the other person, and you're just stopping short of apologising for doing your job. Try to notice if you do this, and maybe spend a week trying to eliminate it and see how that goes if it is a habit you have.

If none of this is relevant, please feel free to message me privately if you want to elaborate on your situation but not in public - it's really, really tricky to navigate the STEM world in a way that doesn't mark you as 'one of those hairy-legged, shouty feminists' (which I totally am, but it doesn't go down well). Maintaining a social working environment while not taking any shit is a pretty difficult balance to strike.