This question is based in the UK
(By "in-public", I'm referring to being around other people in general public places such as parties or cafe's, or on a train too)
Often in public I need to blow my nose, however I personally find it awkward, and feel it weird when other people do it. Is there a "standard" that you shouldn't blow your nose in public in certain situations? And if so, how should you deal with needing to blow your nose in those situations?
In general, see first if you can just wipe it with a tissue paper since this is a silent way.
However, if you really need to blow it and you think it can be done quickly and silently, turn your head in other side and do that using a tissue paper.
If it's going to be really loud, it's better to leave the room by saying,
"Excuse me! I'll be back in a moment."
If you have already a stuffed or running nose, come with a few tissue papers and try to look for a seat near to exit, washroom etc., so it can be less disruptive when you leave the room.
As reflected in AJ's response, it needs to be discreet, and where possible to politely absent yourself to carry out the function. Most people will not be offended by this approach.
If you are in a situation where excusing yourself (on a bus, etc.) and the blowing of you nose is a less offensive/threatening action than a runny nose, etc.; then in as quiet and discreet way possible, blow your nose (with tissue or handkerchief) and offer a quiet apology to those nearby.
