Because, "Duh."

"Duh," a word, yes it is an official word, means to comment on an action perceived as foolish or stupid, a statement perceived as obvious. In other words, duh, assumes that there is a standard we are all on board with that someone may not have understood fully, therefore the only way to sum up the ridiculousness of it is in three letters, "duh."

Example:
So, if it's going to be cold at the pumpkin patch, should we bring our coats?

Duh.

So, if you guys are bringing the pizza, are we eating at your house then?

Duh.

How come when I put too many towels in the dryer at once, they take forever to dry?

Duh.

The "duh," isn't as much necessary as is the gap in time for the other person to recognize that what they just said is a lot more obvious than they thought. The "duh" is there to trigger the person to recall what they just said, and if they missed something, or the words themselves didn't come out right to reiterate.

For example, on the first statement, "If it's cold at the pumpkin patch, should we bring our coats?" An obvious enough response is warranted. Yes, you wear a coat to stay warm in cool conditions. However, the person might be stricken with the "duh," only to reiterate the question as "No, I mean, are we indoors or outdoors most of the time, because I don't want to carry around a coat if there is heat." Ahhh, OK, now the person who responded with a "duh" understands the validity of the question. Again, a "duh" was nothing more than a gap in time, a recognition of a seemingly-obviously answered phrase.

 "Duh," can also be useful to avoid deeper consequences in life. If "duh," is referring the speaker that what they said was an obvious answer, then we can use "duh" on ourselves to remind us of really important things in life. I use "duh" on myself all the time when I start to deviate from my purpose. If someone sets out to be a doctor, though they don't get their studies done because of their passion for drawing, then a "duh" is warranted as to what the person is truly passionate about. If I claim to want to be healthier, yet drink beer every night, avoid the gym, and think a McGriddle every morning for breakfast is a "good" choice, then a "duh" is warranted for how obviously against my goals I am living.

"Duh," can seem so offensive, but typically it is to a person with their own problems going on. "Duh," is totally helpful and can reiterate how obvious, yet overlooked something is.

When I saw people for nutritional counseling, I would be amazed at how much common sense was taken away by influence of a commercial or person at the gym, or even through rationalizing. Things like a "diet" being a temporary thing thus resulting in problems once the "diet" is over. People feeling like a number will make them happy "just another 5 pounds," only to hit them with the "duh" once their goal is met and they are not satisfied. Eating a pizza and beer the night before I met with them, to have them complain about "holding water," a typical bloating response to highly refined, sodium and glucose-rich foods.

All "DUHS"

If a friend is willing to hit you with the "duh" versus the alternative of making fun of your obvious lack of awareness or worse, letting you believe the misstated phrase you just said, then they are good people. The people unwilling to point out the obvious to others can be self-centered jerks whom take versus contribute to society.

"Duh," those three little letters, have so much purpose, so much meaning. Sit back, think about how many times we've avoided pain because a friend or colleague hit us with the "duh." I can only hope the loved ones in my life care enough about me to reiterate my obscurities or the missed punch-line of a joke to follow-up with a "Duh dude."