The best defence to a criminal harassment charge will depend heavily on the circumstances of the offence, however, one common and effective way to tackle a criminal harassment charge would be to argue that the complainant’s fear was not reasonable in the circumstances. That is, you can point to the nature of the relationship between yourself and the complainant, or the nature, context, and history of your communication to show that there is no basis on which he or she can reasonably claim that your behaviour was threatening or harassing.
Alternatively, you could also argue that you did not have the mental intent required to be guilty of this offence. More specifically, you could argue that you did not mean to make the complainant feel harassed or afraid, and that you did not know that your behaviour would reasonably cause the complainant to feel fear. However, in order to successfully raise this defence you will also have to show that you were not reckless or wilfully blind as to whether your behaviour would make the complainant feel harassed. You will have been reckless or wilfully blind if you deliberately ignored or failed to seek out reasonably ascertainable information that would clearly show your behaviour was disturbing the complainant.