Whats the big f'n deal?!

My SO has a best friend that comes over almost everyday. Last night, he came over with his 6 year old son while I was making homemade quesadillas. Out of courtesy (and because they're like family) I offered them some dinner. The kid and my SO said they weren't hungry at the time, but my SO bestie said he wanted a quesadilla. I hooked up the food for my daughter, the friend, and myself. My SO gave me a go to hell look and started acting VERY strange. Even my 8 year daughter noticed. After they left, I asked him what his deal was. He said I disrespected him and what I did was messed up. Really!!?? I thought I was being polite. I would've been happy if he did that for my company.