Yes, it's just a (slight) lisp, not a stutter.
Look everyone, I know Vincent is probably a really nice guy who sees the lighter side of things, and probably this is what the young Louisa needs in their training. He needs to 'coax' the hidden talent out of her and perhaps the funny, loverman apporach is best.
But this is from the horse' mouth. I have recorded the ITT into my harddisk and after playing back the clip, that's what Nicole actually said, "Vincent was the joker in the group today and he was quite distracting to everybody else... Everybody else really wanted to get on with it and learn it, and we were always waiting for Vincent..."
Then we saw her imploring, "Vincent, please!" as if to get him to behave. To his credit, Vincent apologised.
Then it cut to Nicole saying, "(If) they don’t get their act (together), then it’s up to them..."
I am not saying Vincent is a bad dancer. In fact, in the clip, you actually could see Vincent teaching Emma (and Darren) the steps while Nicole showed Louisa her moves.
Don't think Nicole has an axe to grind here (why should she?). I just feel Vincent should give the Nicole some respect. He is a pro after all and I saw the clip in youtube that he and Flavia were teaching the group Argentinian Tango in the previous series, so he should know.