[Carriage Hill]

Back in the mid-60s high school, “plonking” was a nice way of saying ‘screwing’, or the f-word. Maybe it’s got a new definition these days?

[JRandomFreeper]

In the 80s, it meant ignoring all postings by an individual, which may reflect on the meaning you describe. ;)

I had programs that would strip out certain posters from mail-lists and newsgroups that I subscribed to, back in the 300 baud days.

/johnny