To me personally, there’s a difference in calling it that within your group of people, whether it be family of your slimming world group as people can clearly see it is a joke etc. For someone who is an influencer, blogger etc to nearly 40k followers, people who are lacking in self esteem, no confidence, and have joined slimming world to only better themselves, and to then see it be called ‘chub club’, can cause even more negative feelings about their weight and feel even conscious about joining ‘chub club’. Saying that on social media does not promote positivity about slimming world and changing your lifestyle for the better, in my opinion.
I don’t see any issue with it within your group etc and I’m not having a go at all, I’m just saying how it can look and how it looks to me when it’s posted like that on social media