Just ignore them. Block chat block chat bubbles block image. Report them if you want, reporting would result in them either getting a warning from Pokerstars or being banned from chat for a period
I see this cancer comment quite a bit and not only on freerolls I have been told this and similar pertaining to my dog, mother, father on $7 and $15 spin n gos.
Just plain disrespectful and foul mouthed players. In my view Pokerstars should ban them from playing. Unfortunately the max punishment is being banned from chat.