The story of Tuco's reputation.
Tuco is a hothead, thinks of himself as a boxer. The fact is Tuco can't even punch very hard. He sure can swing with all his might. The punch will carry the courage of his heart. But it will never be as impactful as the delusion he carries in himself.
The issue isn't with Tuco discovering his weak nature as a boxer. It is rather about no one is ready to let him find out. Think of it as a "Monkey see, monkey do" kind of a situation. All it needs in one simple incident to cement Tuco and his reputation as a boxer. And just like that, it could take one simple incident for it all to fall apart.
Think of it like this; one fine day Tuco gets into a brawl. We already know Tuco is nothing but a sack of hay. However, he is outnumbering his opponent. Given the picture of the situation, the opponents suffer a staggering defeat. Tuco is the commander of his team. So once everyone on the enemy team is weakened, Tuco takes the last shots to leave a message. Boss style.
When word goes out, no one cares about the entourage. Everybody simply knows that Tuco did all that. Tuco is now a hardhitter. The final blow is what everyone sees. And the final blow was landed by Tuco. So now Tuco walks with his fists clenched, chest pumped, with a killer look.
Add the Tuco's pompous bravado with the scenario, no one ever messes with Tuco anymore. And since everyone stays away from making trouble with Tuco, those who can out-punch Tuco stay away too. Now Tuco is a hotheaded boxer, and everybody thinks so.