My sister invited close family member out this weekend as was going to see an events with big group of friends. I had organised it. Family member rattled off everything else she was doing that weekend, she said she would see 
I cooly said it was fine, I was going with a big group and just to let me know... normally would have fallen over myself saying doesn't worry at all, not to rush etc etc. She is a bit like an older sister to me - both 20s, no kids.
She seemed bit taken aback by my reaction