Discouragingly means ‘in a way that makes you lose confidence or the will to continue.’ You put it on how something happens, or how strong something is: progress is discouragingly slow; the room looked discouragingly empty. It is a writing word. Though actually, in speech people usually keep the shorter form — That’s discouraging — or they say in a discouraging way. You will see the -ly word in news and essays more than you will hear it on the bus. It is about confidence, not about rude manners.