We frum Jews are often very critical. Not that non-frum people aren't, but for us it is built into our system. We have LOOOADDDS of rules to follow and are taught from a young age that whomever doesn't follow the rules is doing something very wrong. This is correct. We HAVE to follow rules and we strive to build a society predicated on self control, discipline and subjugation to a Higher Power. This is very demanding but is our raison d'être [I thought I'd throw a little French in there to keep you on your toes]. Sur tes orteils ["on your toes" in French].
When it comes to ourselves, the notion of having a high bar and elevated expectations serves to help us grow. There are few things worse than a person who is emotionally and spiritually stagnant. The excitement and exuberance of life comes from a feeling that we are not just running in place, coming from nowhere and going nowhere, but that we are on the road to perfection. The Torah is called in numerous Psukim "Derech" which teaches that life is more about the PATH than the destination. In Tanach there are no explicit discussions of the afterlife for various reasons, one of which is that what happens "there" is Hashem's business. Our business is grow in every way possible right now and here. The word for happiness is "שמחה" which is related to "צמיחה" - sprouting. A person is happy when he grows and expands. שמחה is engendered by צמיחה. When we get there, we have GREAT delights waiting for us but that is not our focus now. Our present focus is the PRESENT. Doing EVERY MOMENT what is required of us by our Creator.
On the other hand, the high standards we set for ourselves often cause us to be critical of those who are not [in our eyes] on the level they should be. So we criticize, whether verbally or in our minds.
Here are a few things to think about before you voice criticism.
1] One critical remark can remain with the person for a minute and then he can move past the pain. But it could also ruin his day. Or week. Or month. Or year. Some people heard one critical remark that caused them pain for the rest of their lifetimes. Think about it - we all know that ONE SINGLE traumatic experience [such as sexual abuse רח"ל] can wreak havoc on one's emotions for decades and after countless therapy sessions that person is often still suffering. We are very fragile beings. We DON'T find same effects from the converse - that one positive experience and a person is happy for life. But the opposite - one negative experience and one is scarred for life - is very common. So are the facts of life. So exactly HOW fragile is your friend? You can never know... We ALL fake it to a certain extent and so is required in order to be accepted in society, so it is impossible to know exactly how much your words and actions are effecting others. So be careful. You never know how much pain your words will inflict. Words that you LOOOONG ago forgot about are likely STILL lingering in someones else's mind, causing pain and distress.
2] When someone is suffering in other areas - shalom bayis, parnassa, raising children etc. etc. a critical comment inflicts not only the pain of the actual words spoken but makes the other struggles seem even more painful and challenging. The person feels badly enough as it is and then these words are like the straw that broke the camels back. We almost can never fully know all of a person's struggles and pain, so be careful. You might be rubbing some painful salt into open wounds.
3] Criticism should of course only be offered if it is constructive and not destructive. It will only be heard as constructive if the person giving it loves the person he is criticizing. Does the subject of your criticism feel that you love him/her. No? Then it is probably better not to say anything.
4] Most people get defensive when hearing criticism and it is thus ineffective and doesn't achieve the desired results. It is worthwhile to douse the criticism in a HUUUUGE tub of honey. By that I mean that both before and after there should be many compliments and words of appreciation for this person's character and deeds. This relates to the halachic concept of "ביטול". Be מבטל the bitterness of the criticism in the sweetness of praise. If couched in those terms there is much more of a chance that the person will be receptive.
5] Reflect - Is this criticism about the OTHER person and for HIS benefit or is it about me and my feelings. We often hurt others under the guise of trying to help them when it is really just about ourselves and our own feelings.
6] Reflect - Am I perfect in the area in which I am criticizing the other person? No? Then maybe my energies should be extended instead towards perfecting myself. It is MUCH EASIER to criticize others than it is to change ourselves but our primary responsibility in life is to fix that person who shows up in the mirror every time you look into one. To help the other person save face and to maintain his or her dignity it is worthwhile to point out our own shortcomings to the other person to make it clear that we don't mean to imply that we are perfect while the other person is flawed. The unspoken implication of criticism is that "I am put together, doing the right things in life while YOU are messed up." That is PAINFUL to hear but we hear it.... Make it clear that you ALSO don't completely have your act together and you own behavior leaves much to be desired.
7] Onaas Devarim is an איסור דאורייתא. Any words that cause another person unjustified pain are strictly forbidden according to the Torah. So just as we wouldn't think to put unkosher food in our mouths we should be equally careful about what comes out of our mouth.
A shiva assar bi-tammuz [this year - shomnah assar...] message to increase love and care among Jews and hasten the building of the Beis Hamikdash.