I just got off the phone with my boss, talking about an upcoming project that could prove to be a little difficult in terms of meeting the client's needs for location. As we started to briefly discuss this point, I said to him, "well, we can burn that bridge when we get to it." I looked over and saw my coworker looking bemused, and it was really only then that I realised that, aside from a mention in a Dresden Dolls song, the only time I'd ever heard people use the expression that way was in my family.
There are plenty of other phrases I use that I know come via decades-old "inside jokes" between my parents and/or their friends. The use of "jelly bun" to mean "very good", for instance, is usually met with blank stares and I don't expect anyone who isn't family to have the slightest clue what I'm trying to say (it comes from "jolly bien" which is a Franglais mix of "jolly good" and "très bien"). But this was the first time I realised that "we'll burn that bridge when we get to it" isn't actually how it goes, just how it goes in the hirondelle household.
How about you? What expressions do you use that are specific to your family, or which did you realise much later are only used by your family?