I hate deep breathing/diaphragm breathing around others, it's loud enough for them and they always ask if I'm angry, upset etc. How do I breathe quieter while still having it be deep?
If your normal breathing is really that audible, it might be worth checking with a doctor. You could have something going on, even as simple as a deviated septum or something like that.
Yeah I have to agree with everyone else. If this is a question you're actually asking, it's probably a question for your doctor, because the actual answer should just be "just breathe dude"
Doesn't have to be physical either. You can think you're breathing loudly and annoying everyone and then hyper focus on that while you attempt to breathe quieter.
How rapidly are you breathing? Are you taking 15 breaths per minute or 50?
If you're breathing in and out slowly at closer to 15 and it's audible then something is wonky with your nose. If you're at 50 just sitting still or casually walking around then you're probably just out of shape.
Do a complete inhale and exhale over 10-15 seconds. Move a lot of air slowly. The inhale should physically push out your ribs and stomach and the exhale should push in your stomach and you should feel your rib muscles hurt. As a bonus you can freak out people counting your respirations.
Some folk like my spouse would randomly take a huge gasping breath. She was, and is, always forgetting to breathe. Since she has started learning to belly breathe and it is starting to become more autonomic her gasps have reduced. That being said she still forgets to breathe.
Like everyone else's comments, if it's actually noisy you should speak to a doctor. But I do deep breathing sometimes when I'm angry/anxious to help me relax, and now my partner is conditioned to spot the very quiet sound of me doing it. I've had a chest cold for the last few weeks and he kept asking if I was okay because I was taking deep breaths.
My point is, even if their breathing is quiet, the sound of someone taking slow breaths can be noticeable. Only tip I can think of is to practice breathing smoothly and regularly. When I'm actively trying to take a slow, long breath I notice it can be quite uneven. I breathe in, that breath tails off and I breathe in some more. That leads to an uneven sound that is more noticeable. If I really focus I can breath steadily and smoothly and it's much less noticeable.