I regret inviting an old friend to a funeral
Do you really mean that? Why do you regret doing that?
He was impossible to sit with and he kept laughing oddly loudly
It's natural to change your mind about inviting someone like that. If you invite the wrong people to a funeral they could end up ruining it.
I need to tell them not to come next time, I think they will fuck something up.
I'm sorry he was such a nuisance, and it was very rude of him to do such disrespectful things. You are the master of your events, so I'm sure everyone would be thankful if he didn't participate in the future.