It's an interjection or exclamation to express disgust or annoyance. Buf puf is onomatopoeic noise, i.e. written imitation of a natural sound, which in this case expresses a rejection or discomfort before something unpleasant.
buf is incorrectly written, and should be written as "Buf!" being its meaning: Interjection that denotes discomfort, tiredness, boredom, hot flashes, heat, grief. 2., repugnance, disgust, satiety, nausea.