From Longman Dictionary of Contemporary Englishpooh-poohˌpooh-ˈpooh verb [transitive] informalSTUPID/NOT SENSIBLE to say that you think that an idea, suggestion, effort etc is silly or not very good He pooh-poohed herbal remedies at first.→ See Verb table
Examples from the Corpus
pooh-pooh• Energy companies have pooh-poohed the seriousness of global warming.Origin pooh-pooh (1700-1800) pooh 