(Noun)1 quack
2 one making usually showy pretenses to knowledge or ability : fraud, faker

In Context

“Don’t let the egomaniac charlatans on internet umbrella forums tell you otherwise: there’s no such thing as a perfect umbrella.”

 

 Andrew Goble, GQ, “The Best Umbrellas Are Tough Enough for Downpours and Cheap Enough to Lose Without Crying,” 2 May 2018