If one uses a disco laser or laser pointer in the visible wavelength range, it’s hard to inflict permanent blindness with it. During the time it would take to inflict thermal damage to the retina, reflexes kick in and the person looking into a laser will close their eye and turn their head.

Occurrences of permanent blindness are rare. This study, even if a bit old (2015) introduces the topic with helpful case reports, for example:

Two young soldiers (Cases 1 and 2) aged 27 and 28 years respectively, serving in the Oman army, projected penlight like devices emanating bright blue-green light into each others eyes (left eye for Case number 1 and right eye for Case number 2) for about 5–10 s. They competed with each other to determine who could bear the light longer while celebrating the success of a local football game.

Basically, they did the utmost stupidity: forcing oneself to stare into a laser at close range. They paid a price and damaged their vision, but didn’t go blind from it.

Of course, it’s a different story with cutting and engraving lasers, and lasers outside the visible wavelengths - you can stare into those without any reflexes helping avoid damage. The same article mentions another source, reporting about a guy (also military) who looked into a high-power range finder and perforated his fovea (the area where high-resolution vision occurs). It was most likely an infrared laser.

So, be careful but disco lasers won’t strike a person blind.