To me this little boy seems quite boisterous and a bit of a handful. Whenever there's trouble going on his name is mentioned. But my son seems to like him so I try not to say anything except he knows how he should behave. Today during our bedtime story my son brought it up that this boy had tried to shove grass in his mouth and said 'eat that dirty pig'. When I asked if it upset him he said yes. When I asked if I should tell his teacher he said yes. The boys Mum seems really nice. Would you talk to her or go to the teacher? My son is no angel and there may be another side to it but I have never known him to be nasty in this way
I would ask the teacher about how they are interacting. I'd mention that it seems like there are some conflicts and ask if they have noticed any. If they say they have, I'd ask how they handle them. If they haven't, I'd ask about the incident that your son described.
Even if it seems like the kid can be "nasty," young kids can be impulsive without meaning any harm. It's possible that's what's happening for this boy. The teacher should be aware so that he can help this boy develop impulse control and guide him to better behavior. It's possible the school is aware and is working with the boy on it, so I wouldn't go in assuming there's a big issue that needs to be firmly dealt with.