a common misspelling of the word"brushing" if speaker claims to have said "burshin" on purpose then he/she is most likely not majoring in english and probably has a pet cow.
Person1: You needs to be burshin up on ur ninja skillz
Person2: you mean "brushing"?
Person1:uhhh..no i meant "burshin" cause im cool like that
Person2: Do you have a pet cow?