ADDENDUM - some Britishisms I missed:

• omnishambles

• twattery

• arsemonger

• arseling

• bell end

• hat-tip Samantha Clark: “You forgot Bawbag. For the benefit of our American chums, ‘bawbag’ is a Glaswegian term referring to the scrotal sac, ie that which holds the ‘baws’, specifically not the baws themselves.”

• Advanced skill - [random household appliance, storage item or DIY household tool] <-- for example, "OH SOD OFF YOU ABSOLUTE SPANNER" or "YOU UTTER, UTTER SUITCASE, WHAT DID YOU DO THAT FOR?"