A typical 'Lock Stock' word would be ...
Muppet A foolish or stupid person
eg: "Don't be a muppet, I can't believe you're gonna do that."
1. To describe someone mad and wacky, or stupid ie you are such a muppet.
From the late Jim Henson's "Muppets - mad, zany puppets who had their own show for many years and also
played a huge role in the success of Sesame Street.
2. A fool, someone who is easily controlled (like a puppet ... hence muppet!)
'Muppet' is now a recognised term, appearing in the latest edition of the 'Oxford English Dictionary'. The OED meaning is listed as 'foolish person'
NB: Muppet in the Dublin/Limerick area of Ireland means hippy or alternative music fan (according to an Irish colleague)
NOTE and SPECIAL REQUEST
My particular slang area of expertise is London/Estuary English ... if there are any other Brits on the list who have any other BritSlang to share, please let me know off list and I'll include them in future posts (with full credit to the provide of course).