A young girl I know has just put on Facebook that she won her first stone award in Slimming World, the biggest "but" offender I know has commented "that's great but just remember it's about healthy eating too" 
Now I'm not into group diet things at all but isn't that pretty much the whole premise of it? I just find it so buzzkilly!
Same woman has done this countless times about everything. When I finally bought my first car "but just make sure you're still getting exercise"
When I got a pretty big promotion and was delight "brilliant, thrilled for you but remember it's going to be a lot more work than you're used to"
There's so many examples and I never really know what to say because she's coming across helpful and happy for you, but it just feels like a bit of a mood killer!