This information was given as a response to a request for "boo! hiss!, However Klingons vocalize their displeasure when in a group" (the KLI word list links here), for which we learned that baQa' is used for this purpose. boQwI' and the KLIwiki both include "boo! hiss!" as glosses along with "general invective". (My suspicion is that this is just a specific usage of a more general invective, rather than the sole meaning of baQa', but of course I'm not MO.)