We have some things I think are only said in our family.
For years & years, B has said that he's "walking my goat" when he's teasing me, or when I'm being gullible about something. I really have no idea where it came from, but now even the boys say it. strange!
When we'd go shopping with my sister when the boys were much younger, sometimes she'd stop to look at something and we'd move on ahead. One of the boys would ask where she was, and I'd reply "Oh, she joined the circus." Now that they're older, they are sometimes the ones who fall behind, and we still say "Oh, he joined the circus." or "Did C join the circus?" It's a hilarious joke to us!
I have always said the "straw that broke the donkey's back." Everyone else insists the phrase should be the "straw that broke the camel's back." BUT, how often do you see a camel outside of a zoo in the United States? When you think of a work animal, don't you think of a donkey? There, case made ;) B has his own, too - he always says "better than sliced pie" and I insist the phrase is "better than sliced bread." Who buys sliced pie? But when you could buy bread sliced that was an innovation!
When my sister was a toddler, she called Cool Whip "whip top." To this day (she's almost 27) our entire family STILL calls it "whip top."
I'm sure I'll think of more, but those are the ones I can remember right now. What are some of your family's sayings?