By switching the first letters of "damn" and "family", you can say the whole, entire, freakin' family is coming without actually cussing.
Usually spoken in redneck and/or back-woods families, where the family can be less than desirable to be around.
Dude ... is your ENTIRE family coming to the wedding?
A combination of the words "family" and "damn," placed in such a way so that friends and acquaintances who have heard you refer to yours can mistakenly mix the syllables and call them your "damn family".