Unfortunately, some people use it to be snide, so its unclear and should be avoided. Some think that adding a 'smiley' is a license to be tactless, blunt or insulting, but it's better to learn how to express ones thoughts properly. 'just sayin' serves the same faulty purpose. If you feel the need to add one of those to avoid being misinterpreted, rewrite your statement. 'not trying to be harsh' or 'please take this as constructive criticism' are more expressive.