Why people become irritate because of their depression?

In a DEPRESSED state a person is MISERABLE & worried,
which makes the person angry

Wow, that's hard to explain. The particular reasoning for each person is different. For me, I just don't want to be bothered with anything other than my thoughts. I get irritated that others would try to 'cheer me up'... that they are standing too close... that they are in the same state... that they want attention... etc. The triggers are different for everyone.

The thing to remember is that if a person is depressed and irritable, they usually don't mean to lash out. They don't mean to hurt the people around them, they just feel so bad and are so numb that they just act without thinking (and then feel guilty for having yelled at someone).

Of course, if they are so irritated that are violent towards you, you should seek help immediately.

it is mostly normal for everyone to feel irritated while depressed. because while one is depressed he/she goes in a variation of mind and his/her mind will not sand or be erect on any topic. mind will always be in a motion and will not be withhold on any place. the mind never realizes what happens outside but is always depressed and thought is triggered insid the mind. if any person is depressed and one goers and complaint or atleast speak softly, he/she just feel that they are annoying him and just explodes himself. so in most cases this happens because of high bp. its something like ur mind and brain reflects and vibrates or even stimulates ur pressure.
this is a common problem and can be cured if you find the peace of mind on anything , anywhere but shud be harmless to anyone

Well, Isha the thing is so that one's depression is already a painful thing, apart from this it is everyday in one's mind & taking the pain of this sadness makes a person more & more depressed & turns him or her into frustration, which irritates a lot.

because nobody understands their problem the way they see it.

because they have no control over their emotions.

because they are unable to find a solution to their problem.

Maybe it's because they're too afraid to tell you something or plainly are just paranoid somehow?

Well it's because most people who suffer from depression don't understand it.

cause when one is depressed everything and everyone around them is an annoyance

Some people experience anger and irritation when they are depressed. It's just another symptom.

This is due mental bi-polar disorder and u need to consult a good doctor.