Dar para el pelo

[poli]

I think it means slam somebody, or to whoop, or shellac someone, but certain internet sources indicate that it may be a mild reproach. What do you think?

[CrOtALiTo]

It gave anything for the hair.

A shampoo?

[Rusty]

Poli, I verified a lot earlier today that this is a mild reproach - stop that or I'll give you what you deserve - but I think it could certainly come across as a harsher warning depending on the tone used. Your other translations seem to fit that category.

[sosia]

Agree with Rusty.
Only the context or the tone shows how hard the "I'll give you what you deserve" is
saludos :D