Let's have a quick etiquette/politeness/simple manners rundown here. You meet someone, you say hello; you receive something, you say thank you; you cough, you cover your mouth.
Simple. Basic. Easy.
See, when I'm in the metro - not a mood-positive to begin with - and someone coughs right in my face without covering their bloody mouth ("bloody" being an unfortunate figure of speech at this juncture, but what the hey, I'll leave it in, it ties in well with what's to follow, consider yourself warned), it makes me want to charitably reach down their throat and rip out their lungs to get them rid of whatever it is that is obviously hindering their breathing so badly that they don't even have the strength to lift their hand to their mouth. Desperate times call for their desperate measures, what can I say.