laugh down
To dismiss, belittle, or reject someone or something by laughing derisively or treating them or it very casually. A noun or pronoun can be used between "laugh" and "down." There were quite a few doubts within the company about the decision, but the new CEO just laughed it all down. For the most part, people here just laughed down the foreign president and his blustering rhetoric.
laugh someone or something down
to cause someone to quit or cause something to end by laughing in ridicule. Her singing career was destroyed when the audience laughed her down as an amateur. The cruel audience laughed down the amateur singer. They laughed down the magic act also.