Yes ok it is offensive, so if you are easily offended this doormat is probably not for you (or your friends). If however you are not easily offended and are a bit tired of people visiting just when you want a bit of time to yourself then you need this doormat. Any visitors should hopefully get the message and F Off. If not it's probably your mother popping round with some soup, so you might want to open the door and apologise.
The F Off Doormat is for unwanted visitors, so place in your porch and they might just get the message!
Not recommended if you have children visiting.