to place one's face between a woman's breasts and to exhale sharply while moving one's face quickly from left to right.
The girl I was with last night had big titties, so I gave her a brumsky.
After putting your face between your lady's breasts, move your lips back between them while loudly saying "bbbrrruuummmssskkkyyy...”
Properly done, it should last at least 20 seconds or more.
She had never had a brumsky before. So I gave her one, and we both had a very good time with it.