If an act is discreditable, it is bad or wrong in a way that makes people lose respect for you, or stop trusting you. It is not only a small mistake. It is the kind of thing that hurts your name. News, school reports, and courts like this word more than everyday chat does. We often put it on the deed, not only on the person: a discreditable lie, a discreditable use of money. Shameful and disgraceful sit nearby in feeling, though actually discreditable points more at lost trust and lost standing than at a red face. If something is only embarrassing, this word is probably too strong.