To co-workers with sniffles:
STOP SNIFFING THE SNOT BACK THROUGH YOUR SINUS PIPES BACK INTO YOUR THROAT. Pick up a tissue and get rid of it, instead of doing this every 5 minutes. It’s disgusting and distracting. If you find that you’re having to blow your nose too often, you’re sick and shouldn’t be in the office anyway.
Your cow-orkers are only snorking every five minutes? Lucky you. One of my neighbors has some sort of chronic condition and snorks, snuffles and gurgles all day long like a percolator at a PTA meeting.
As someone with chronic sinus troubles *and * as someone who is revolted by the horking, snarfling, and sniffing of others, I sympathize with both sides.
It is true that in some cases a simple nose-clearing would end (or at least postpone) the sinusal symphony, but as I’m unfortunately now aware, some conditions can cause a near-constant flow of postnasal drip, even when there’s no corresponding infection. In my case it’s resistant even to allergy and sinus medications (and blowing doesn’t help much).
So there is at least a chance they can’t really help it. Not that that mitigates the frustration and digust much.
My favorite musical - The Sound of Mucus.
I especially like a nice chorus of it at a restaurant, an art perfected by old white men.
True. As I am bitterly aware. I’ve currently got enough antihistamines and decongestants aboard to stock a drugstore; and still the eyes tear up, the sinuses feel concrete-filled, the mucus flows, and the overpowering need for repeated bouts of snurfling, hawking, coughing and snorking – which provide perhaps a few seconds’ worth of relief, if even that – cannot for long be denied.
Fortunately I work at home, so am spared the further indignity of haplessly inflicting the outward signs of my suffering upon suffering innocent coworkers. Those of you who hate such snot symphonies, I sympathize, believe me I do. But how would you like to spend your every waking hour, for days, weeks, months at a time, afflicted with the symptoms of a severe head cold, unable to find much if any relief in any remedy, and without any hope of the condition abating for good?
And the spring allergy season is just beginning for me… 
If the problem is truly in the sinuses, sniffing is often effective where blowing isn’t. When you sniff, you’re creating a partial vacuum, drawing out the mucus from within the sinuses, when you blow, you’re creating pressure that might push it back in or just make it stay put.
Sometimes, only a gross snorty sniff will do the trick, however, I think time and place should be carefully considered.
You might get better results if you directed your comments at the offending parties. Don’t be scared . What’s the worst that could happen ? You get a bugger wiped on your shirt ? 
I’ve tried, but he’s oblivious to the noise he makes.
On a related note, who’s worse: Mr. All-Day-Sniffles or Mr. Won’t-Clear-My-Throat-But-Will-Continue-to-Talk-in-a-Phlegmy-Semi-Mucus-Gargle??
And as for the neighbor of gotpasswords, these humanoids are impossible to be in the presence of. I remember working out at the gym and a guy decides to use the ellipto-trainer beside me. Not five minutes into the workout and he begins a series of burps, gurgles, honks and other miscellaneous emanations that I cut my workout short and let him have the place to himself. Oy.
Amen!
(I’m sorry, sinus people.)