funny - something or action that brings a laughter out of you. strange - something or action that is not of the norm. weird - something or actions that is more than just strange.

I believe they can be used interchangeably depending on the context. Someone who is doing something weird or strange may seem to be funny to an observer. A person doing something weird that’s not normal may be interpreted as strange, but again whether it’s funny is in the eye of the beholder. Something strange or weird isn’t necessarily funny. The man acting strange over there is very funny. He makes me laugh. How weird that woman is dressed as a dog sniffing a tree. That is strange behavior. I woke and heard a strange noise. It scared me, but thankfully I fell back to sleep. In the above sentence you would not use funny in place of strange. You could use weird but strange is more fitting to the description and reaction.