Don't disrespect the lord like that

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I just had the most..awkward conversation ever lol 
I'm at my friends house, she's a lot older than me so her mom is in her late 60s 
She's this little old lady dressed up in this incredibly bright yellow laced dress because it's Easter. Okay. 
I feel like crap, my legs are killing me for whatever reason and I am chillin in my PJs 
I thought about getting up and putting my jeans on but I don't want to move because of my legs. So I'm sitting here on the couch watching fried green tomatoes and she goes into how her family always dressed up nice for Easter Sunday because it was disrespectful to the lord so I should go and dress up. 
I just told her.. "I'm an atheist, so um.. I feel like I can dress how I please..." I said that like so respectful though but I was being too straight forward I guess and now she's mean mugging me.
Everyone else is in jeans and t shirt, the men are in basketball shorts and are sitting in the mancave playing video games. Her daughter put on casual clothes and did her hair. 
Nobody here has a problem with the way I am dressed but her... I don't exactly know what else to say to her lol.