It's just a lame attempt to get you to compliment them.
I like the idea of agreeing with them... maybe even add in that the extra weight is bad for their health? LMAO
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“All his life he tried to be a good person. Many times, however, he failed.
For after all, he was only human. He wasn't a dog.”
― Charles M. Schultz
Warning: The above post may be dripping in sarcasm and full of smartassedness.