perhaps "nice" is the wrong word to use? Maybe the word "friendly" is more fitting?
Nothing wrong with speaking your mind but some people seem to drive it home that they are not bothered about upsetting people just so they can have their say on something, even when that something has no relationship or bearing upon them.

tact is the key word when speaking your mind, we can all say what is on our minds, but judging whether it is useful or appropriate is another skill altogether...