"Vexatious complaints" refers to recurring complaints that are made with the intention of causing trouble, annoyance, or harassment rather than seeking a genuine resolution of a problem. Full definition
To do so would only encourage vexatious complaints against MPs and other public figures. (conservativehome.blogs.com)
The ban is a thinly veiled attack on Humanists UK, and is designed, in Nicky Morgan's own words, to «stop vexatious complaints against faith schools by secularist campaign groups». (humanism.org.uk)
It was a gruelling fight, however, involving years of litigation (in both the United Kingdom and the United States) and public hearings, as he fought back with vexatious complaints. (briandeer.com)