The problem with approaching people with the assumption that F=offended, and T=not offended is that instead of identifying the actual functions they are using, it can be easy to encounter an offended person and then label them as an F after the fact.
A sense of being offended has its roots in internal expectations about how another person should act. If there is a range of behaviors an individual considers off-limits or unacceptable whether this be stupidity, moral repugnance, impoliteness, up-tightness, mean, annoyingly happy or helpful, or whatever, it is the thwarted expectation that creates the offense. Both Ts and Fs express expectations about people and annoyances when people fall short of these.
I think there is a tendency for different types to be offended by different sorts of behaviors and ideas. People who use empathy fully can be quite difficult to offend because they *get* why the person is acting out. The more you can glimpse the world from someone else's vantage point, the more you realize almost nothing is actually personal. All behaviors are based on cause and effect within that person's life. To quote Thich Nhat Hanh "This is like this because that is like that."
(Anyone who think T's can't be offended, just insist on something being true and holding them accountable to an idea they think is dead wrong/stupid; and you'll see how quickly tempers flare. I know I tend to be more offended by someone saying something untrue about me vs mean about me.)
People tend to be good at targeting exactly what another person holds as most important. At work I have sometimes been torn to shreds by clients who have personal/mental issues. The way they target me is often discrediting me in a professional way. I notice that people regardless of intelligence level or other issues can be quite skilled at knowing exactly where a person's places their best energies and uses that as the avenue to discredit. People are skilled at offending. Every time I look deeper into the situation, it becomes clear that the attack is more an outpouring of their own stress and emotional states than anything related to me. People often approach one another as a blank canvass upon which they paint their current emotional state by distorting their perception of you to make their negative internal world seem coherent. Responding to offense by quietly observing can offer a great deal of understanding about what it is like to be another person.