This has happened to me several times on the SNA to PHX flight.

In one instance, the crew had handed out peanuts to just about the entire plane before the lead FA announced that someone on board had a peanut allergy and all the little bags of peanuts had to be collected. So, the FAs came around and collected the bags of peanuts.

But, I do have to wonder how people with peanut allergies even get to WN gates at PHX T4 considering you half to go right past a Cold Stone Creamery that has a very strong peanut aroma wafting from it and through that end of the terminal.