Say,this kid is doing DLs and his back is horribly rounded...Would you step in and correct his form?
Or you just mind your own business?
approach him and advise him lo.
if he still do den MYOB. no point telling him or reminding him again.
unless i'm the gym instructor on duty otherwise no.
My basic guideline for deadlifting.
1)Tilt head up
2)make chest proud and arch back
3)bent over with knees relaxed.
Keep 1) and 2) throughout the whole movement until done.
I probably wouldn't unless it was really really bad and he was in immediate danger of hurting himself.