Kevin Smith does seem to hold grudges but it seems he had more than one run in with her. Kevin Smith's Reese Witherspoon stories.* On the other hand one could say that those incidents were many years ago when she was a young actress just starting out.
*Warning for language some may find offensive.
Well, yes, but I have to say, that explanation actually makes me less impressed with Kevin's position. Basically, his complaints boil down to ego trips. First meeting, she compares his movie to a movie he hates, so he's mad. Then she's rude to his girlfriend, so he's mad. Then she says she doesn't like his work. So he's mad, and now calling names.
There seems to be precious little of his dislike that is based on her character, and a whole lot more based on the fact that she's not overly enthralled by him. Which, I have to say (and I'm a Clerks fan, so Kevin is okay by me), if you saw Clerks and Legally Blonde side by side you wouldn't, so much, think the same people might be into them.
I think Reese AND her husband messed up royally, I think they are massively unfortunate that their error, which is made every day by any number of other people, gets the extra-hot spotlight because of her celebrity, and like anyone else who has had an episode of massively poor judgment, I hope they learn from this and wish them the best for the future.