Apparently we enjoy telling people off. It's a scientific fact!
However, being pleasant to people can also have benefits to both parties! Links below.

As in many things in life, there are right ways and wrong ways. In the last few months, on three separate teams I've seen evidence of this. In two instances the team leaders dealt with the issue firmly, effectively and positively; in the other a member, in the absence of the team leaders' response, took it upon him/herself to rebuke the offender in a public and destructive fashion.

Two of the instances revolved around SP's rules regarding advertising and salesmanship, which is sometimes a grey area, and the other around the rules of a challenge which were carefully spelled out to all members beforehand.

I think the team leaders' role was critical in the instances where there was a successful, non hurting outcome. They removed offending posts, circulated members with an explanation and/or reminder of the rules , contacted the individual concerned personally and kept their tone firm and businesslike; implicit in their actions and remarks was an understanding that we can all make mistakes (I forget to put my own brain into gear before doing things all too often!) and that enthusiasm can sometimes lead us astray.Using email also allowed the SP member involved the dignity of a private response.

There was nothing that could be described as "constructive criticism" in the third instance, just a direct order on the post to stop the activity. Another team member had to ask leaders to involve themselves but by the time one responded the offending member had withdrawn from the team and it has now lost her contributions which were considerable. There were no winners here.

My own views on this are to remember always that the written word can never be recovered, so be careful what and how you write, especially if your respondent might be hurt or sensitive to what you write. What might seem to you a quick and blunt reminder might be read as a personal attack. Always contact a leader if there is an apparent breach of SP rules and leave it to them to take appropriate action.
If you have formed a team or become a leader you must be aware of the responsibility, if you lose interest in it or withdraw from SP altogether, of thinking about the team's future; it takes little effort to resign as a leader or to have the team mothballed if no-one steps up to lead. An unmonitored team is a recipe for trouble, and the resultant harm to members is not what SP is about.

Of course, we must obey the rules of SP or the whole organisation will collapse into anarchy, and many of us need occasional reminders about them, but it is important to the community that those reminders don't become personal attacks or the means of relieving our own doubts and difficulties. We might get a kick from telling someone off but we can also get satisfaction from doing it in a non-judgmental "nice" fashion.

news.bbc.co.uk/2/hi/heal
th3601134.stm

mysuperchargedlife.com/b
lo/10-ways-being-nice-is-g
ood-for-you/