Right!
So MiL over the last 3 weeks has decided to go on an almightly slimming world themed health kick. She's desporate to be slimmer for my wedding so I can relate to that! She has about 4-5 stone to lose so she could definately achieve that in plenty of time even on slimming world.
DP and I ate dinner before we went to see them because I didn't want to put any pressure on MiL to cook for me or anything. All good.
We got there at 7:30pm and they had ordered us fish and chips as a suprise treat
.. For context, we lived with them for a year while we saved up to buy our house and fish and chips was a weekly treat. We'd all sit and eat them in front of the TV and have a catch up. Lovely thought, but they KNEW we were eating before we went and that I'm trying hard to shift the weight so just WHY. 
So the fish and chips arrives. THey've ordered each person a large fish and a seporate large chips "because you get more for the same price if you have them in seporate boxes".. I said i appriciated the thought massively but they could share mine out between them. MiL thought it was fine because "it's all covered in fat" 
Anyway, DP and FiL shared mine between them because MiL was "being good" and not having any more. SO I sat there while they ate quite happy and chatting away, absolutely no ill feeling at all about it and was really happy just to see them.
Fast forward 30 mins, DP is about to explode he's so full and keeps giving me the "you owe me" look
... MiL produces the biggest chocolate cheesecake you've ever seen from the ktichen 
Again, I say thanks for the thought it looks lovely but I really can't and I'm still full from dinner.
MiL goes ape shit. "Why can't you just enjoy yourself for once, a bit of cake and a few chips wont bloody kill you!" The tone was jokeyish, but her face said she was deadly serious.
I initially tried to laugh it off and said something like "I know right? it's awful being on a diet at family stuff, but I cant just have a ittle bit that's the problem! You've got much better self control than me"...
But she got redder in the face and was giving me the death stare: "You did this at XXX's bithday as well, wouldnt have a bit of cake with us and everyone noticed" (she's referring to a few weeks ago at a family get together when I had ham and salad ferom the buffet and no cake)...
At this point DP came to my rescue and said something like "Mum you should be encouraging her not having a go at her for not eating cake, she's doing really well and I'm proper proud of her".
Well MiL went a bit redder and said "I'm not having a go at her I'm only saying, she's getting obsessed with it now"
So i basically sort of reassurred her I'm not obsessed with it and I'm being very sensible and the weight is coming off at a stewady rate.
Then she launched into how well she's doing on slimming world (3lbs in 4 weeks so really good effort) and how she can eat as many potatoes and pasta and rice as she likes so my diet was restrictive for no reason etc etc.
I tried multiple times to change the subject but she loves to talk about slimming world (Nando's lemon and herb sauce, only half a syn for a tablespoon!) so i sat through an hour of that before DP decided we needed to leave before I went nuclear. 
Argh!