It would definitely have to be a family thing. . .The Urban Dictionary defines "brunz" as:
1. brunz N. An elderly person. Typically used in a derogatory tone.
and says the "trunz" is undefined.

Joe and I had (still do, sometimes) a language barrier with our growing up in different locales. . .Now I know it's not just where you live, but your family's lexicon, too!