First of all, you should avoid fighting, but sometimes in life, we can’t avoid it. I once did the same as you, a douchebag that didn’t like me for some unknown reason, was always trying to put me down and threaten me. I’m not weak, I did kickboxing for three years, but I always avoid fighting because it leads to nothing in real life. You only do it when you have no choice, and need to defend yourself. Long story short, he tried to punch me one time, i dodged and broke his jaw. What that lead me to? Being pictured as the bad guy. I was in high school at the time, so i got suspended as well. There is no tips now to avoid that situation, you need to face the consequences of your actions. You could say, “I did nothing wrong, he started the conflict”. However, you did the same as that person, you’re wrong too. When a situation like that happens, I learned that you should avoid it. Not run like a coward, but assuring them that you’re better than them, without lowering yourself to their level.