Upon first reading this, my reaction was "How terribly awful of him- you absolutely were insulted and that was completely out of line!"
It's been an hour or so later and upon reflection I agree with others that i think this was a cheesy dad making a bad joke (EDIT: wrote this before reading kaplods' and Unna's comments- looks like there are a lot of cheesy dads out there
). I can absolutely remember my father doing something similar. He's a bit oblivious- he doesn't really see weight, attractiveness, etc so he has certainly made jokes that others- like my mother, who are more consciousnesses - deem as offensive.
Last week I was jogging and I passed a walker who yelled out to me "run faster!" I was at the tail end of my run and was definitely losing steam, so I DID perceive my run as stupidly slow, and therefore his comment as mean. I think I responded with something defensive, like how long I'd been running for or something. (And immediately felt like a jerk for doing so
)
It was totally uncalled for on my part- I don't think he meant to be rude, he meant to be supportive. Or maybe he was even poking a bit of fun at himself for just walking when others were jogging.
That said, I have had people make outright cruel comments before, so I completely understand why this one could be interpreted as such. Once I was in an American Apparel looking at a pair of pants that would have looked hideous on anyone except a 5'9 model weighing 100 lbs when a salesperson came up to me and snarked "Oh are those for your younger sister?" It was an absolutely awful thing to say. People DO say really cruel things sometimes.
I think in this situation though, people -myself included- sometimes just make jokes that in a given context are more offensive than others. I'm sorry that for your sake that happened, but I am very confident (and hope very much) he was just being a goofy, oblivious dad.