Not at all. I don't mind when a user has bad grammar, I don't think there's much you can really do about that though. Most forums you go to you will see many people with poor grammar. Some here are like that, hell even with myself, my grammar isn't 100% perfect, I don't think anyone here is perfect when it comes to their own grammar.
There's also no rules users have to follow when it comes to ones own grammar on sites. It really should be let go, and hopefully the user learns to write better as he/she goes. I think most people with bad grammar would be called out for not being able to understand them, so they might leave the forum eventually.
There was a user at this site I used to mod for (their forums) and one user had the worst grammar I have ever saw in my life. He would post paragraphs are barely legible things, complaining about other users. Other users made a fuss about the way he talked. But, he would start to get frustrated when people didn't understand him, so he started to call people names and get overly offensive, to the point we had to ban him. He cried about that wanting back on the site, but we wouldn't let him.