Wiktionary
a. (context slang pejorative English) Of or relating to such a worshiper or such a church. alt. (context slang pejorative English) A member of a Christian church whose worship is characterized by enthusiasm and spontaneity. n. (context slang pejorative English) A member of a Christian church whose worship is characterized by enthusiasm and spontaneity.
Wikipedia
Happy-clappy, or Happy clappers, is a derogatory term referring to a style of Christian worship particularly evident in Pentecostal churches.
This style of worship involves joyful congregational worship songs, often accompanied by acoustic guitars and drums in which the congregation clap along to the rhythm of the song, or raise one or both hands in the air, and occasionally dance. Christian critics of this style of worship like the former Archbishop of Canterbury Robert Runcie object to what they perceive as simply the rousing of emotion rather than properly focusing on God. Supporters counter that this style is more relevant and therefore accessible to ordinary people.
Unlike many derogatory terms, it has not been adopted by groups that practice it, who prefer to call it "charismatic" or " spirit-led" worship.
Also used to describe someone who is annoyingly happy.
Usage examples of "happy-clappy".
He was a born-again Christian, Scientologist, something like that, or one of the happy-clappy bands.
And no doubt those happy-clappy expressions were virtual fakes painted on bemused faces.