Out of sorts, don't get upset
You could say 'don't get upset', or 'there's no need to get out of sorts about it'.
Note that 'knickers in a twist' is a fairly rude phrase. Saying it directly to someone is always going to be really 'fanning the flames' - not calming the situation. You can't convert a rude phrase like this into something polite without changing its very nature.
Non-rude alternatives are going to need to include genuine care for the person and be calming or assisting the situation.
You may however, harmlessly use the phrase to talk about someone out of their earshot, like 'my boss really got his knickers in a twist about my lateness'. But if he overheard you saying it - that would be baaaad! Sooo. Bad.
Note that in UK English we use the expression about women or men, still with 'knickers'.
Meaning, you can say, even of a man ‘he really got his knickers in a twist over that!’
Why? Well it's even more funny!
Note: I am not talking about ‘who is saying it’. I am talking about saying the phrase about either a man or woman.
Postscript - what ‘knickers’ is really about:
'knickers in a twist' is a way of saying 'I perceive that something, under the surface, unseen, may be troubling you'. You need therapist-level sensitivity, to be able to pull off saying that to somebody without enraging them.
Postscript - the ‘therapy speak’. An alternative to ‘knickers’:
Here’s how to use more powerful language, in this kind of situation. Instead of ‘knickers’. This is the ‘therapy speak’ that I refer to.
‘Oh!’ - pausing, creating a ‘moment’, with the person. Looking at them. Maybe drawing them away from others and towards you, by gently touching their arm, looking them in the eye. Or just pulling them to you with your focused presence. Creating a tiny world, a bubble, with just the two of you in it, for a moment.
Then say, quietly (so that others cannot hear it):
‘Did something touch a nerve?’ Or
‘Are you having a bad day?’ Or
‘Can I help you with something?’ or
‘Is there something that I can do?’
They will then either
- blurt out what happened
- tell you the real issue
- get angry or defensive
They may tell you ‘yes, dropped the damn egg on my tie this morning!’ Or, ‘I feel so bloody frustrated about this report!’ Or ‘things just haven’t been the same since Mary left...’
They may tell you, or hint at a really painful problem, even maybe from their childhood.
All you need do, is hear them. You can squeeze their arm, look them in the eye, smile and say:
‘I hear you’ or
‘I understand’ or
‘Oh, I see’. Or even, just
‘Oh!’ As you hold the moment and look at them.
Feeling and being present to them, in that moment of empathy, is more important than words.
Then you’ll have found out the real reason why ‘their knickers seem to ‘be in a twist’. But without ever saying those words. You’ll know more of what they’re about. And you’ll have been able to help them.
How to say that your knickers are not in a twist (in response to the now re-written question):
- I’m not going to lose my cool about it
- I’m not going to have a thrombie over it
- I’m not going to write to my therapist about it
- I’m not going to lose sleep over it
- I’m not going to spend sixty thousand dollars in therapy over it
- I’m not going to lose my rag over it
- I’m not going to throw a wobbly over it
- I’m not going to rant about it
- I’m not going to cry into my hankie
- I’m not going to run home to my Mum
- I’m not going to stress over it
- I’m not going to need an extra 3 hours with my therapist over it
- I’m not going to run around the room screaming about it
- I’m not going to have to do retail therapy over it
- I’m not going to need an underwear adjustment on this
Optional Personal therapy moment:
Ask yourself: ‘what are my knickers really in a twist about?