* Obviousness: It implies that something is so clear or simple that it should be obvious to anyone.
* Contempt: It can be used to express annoyance or frustration that someone doesn't understand something that seems obvious.
* Sarcasm: Sometimes it's used sarcastically to mock someone who is pretending to be confused or to imply that they're being deliberately obtuse.
Examples:
* "You forgot to bring your keys? Duh! You always forget your keys!" (Contempt)
* "The sky is blue. Duh!" (Obviousness)
* "You're telling me the earth is round? Duh!" (Sarcasm)
Origin:
The origin of "duh" is uncertain, but it is likely derived from the sound of someone making a mistake or being surprised.