Quoting Rumpelstiltskin:" I think I'm the only one so far that will admit I'd be embarrassed and hurt. I wouldn't let him know ... [snip!] ... ). We both know that we will be working out together and eating right together again, but it's not something we say. "
See, if SO was super skinny (well, he is "skinny", but not like what he used to be) and he just came out and said "hey, let's lose weight" I would be kind of hurt, but in our case, it stems from me already wanting it and him taking a weight lifting class for his PE credit in school, so I'm not offended.
But I'm with IcePrincess - my SO like thick chicks, so it would be weird if he worded it in a "weight" kind of way, but luckily we BOTH approached it from a health standpoint. If it had been him and only him and he brought it up to me from purely a weight standpoint, I would kind of be hurt.