Insult is not used as a noun here. Don't insult me = Do not insult me. If it were a noun, you could have asked here "Can I have it?" and the answer should have been - yes. But, that's not it. You get no as an answer. So it's not a noun. But, if you had asked, "Can you do it?" You get yes. So it's a verb. The same goes for trust. I can't trust her. Ask "Can I have it?" No, you can't. So, not a noun here. Now ask "Can I do it?" You get yes. So it's a verb. I hope this cleared your doubts.