Yeah it is, but it maybe shouldn't be. Like, sometimes shit is actually too loud for the size of the club/quality of speakers and it makes you not enjoy the DJ. But I struggle to imagine a way you could communicate that to a DJ in a loud club and not come across as rude. If they are redlighting the mixer then you can point to the red lights though. DJs shouldn't be redlighting.

If you see some red on the mixer. Tell them stop clipping. 😂