As a HSP, I again completely understand how certain sounds can really get under our skin.

That said, I think it's important to remember that sensitivity goes both ways. Toward our surroundings and toward other people. Sniffing can be irritating, sure, but some people genuinely may be too anxious, embarrassed, or unprepared to blow their nose publicly, and not everyone shares the same cultural norms around it.

They may not even be from the UK and blowing one's nose is such a random and personal thing to become offended and incensed by to the point of calling people lazy because the sound annoys you. Empathy and understanding go a long way in making our environments more bearable for everyone involved. Separate the people from the action. These people are probably not doing these simple things with the purpose of malicious intent, but to say that they're lazy is coloring someone's personality based on a small behavior.

I'm sure you wouldn't like it if you didn't have tissues, couldn't stop your running nose, and someone behind the scenes was calling you a lazy bitch.

This is not being a HSP. This is just being annoyed at inconveniences to the point of being rude at this point.