In our modern, fast-paced world, evolution favors those who are able to express themselves concisely with the least effort. Thus, great pioneers in modern communications have invented 'dunba' to replace the phrase 'dont worry about it'.
The evolution of dunba:
"Dont worry about it" -> "Dont worr bad it" -> "Dun bout it" -> "Dunba"
A: Honey, did you remember to give Sarah her insulin shot before she left for Chocolate camp?