I personally never heard nor used it as a verb, but rather as a noun/adjective, and always in its feminine form (bêcheuse).
C’est une bêcheuse could be translated as She’ll bore to death or She’s very annoying. It can also mean pretentious, condescendant, snobbish.
CNRTL for “bêcher” has 2 tabs, the second lists meanings like “to insult”, “to scorn”. However, if you look at the years listed for the sample sentences, you realize that these examples are WAY outdated (1883, 1931). I seem to remember seeing
bêcher with the meaning of “to scorn” once, in a 19th century novel. But I’ve never heard it used “live”, and even bêcheuse is something I haven’t heard/read in the last 20 years or so…