When I lived in UK my coworkers referred to idiots as muppets. Faaaahhking muppet!

This was funny every time to me.

I've used all of those except wheeliebin, which I've never run across before.

Ain't no shame in borrowing good slang, and that's something brits do extremely well imo. It's usually easy to use, rolls off the tongue, and sounds just silly enough.

I'm right chuffed about it

I didn't know these words were distinctly British.

What about knob? "He's such a knob", "Oi, knobhead!"

I’m rather fond of a simple one word response to almost anything that has been said: quite.

I love using "posh". It parses well and its meaning isn't ambiguous.

Other than chuffed and wheeliebin, I think I've used the rest in one or two consecutive sentences at some point in my life

If you were invited to a fancy dress party, would you think you’re supposed to wear a fancy dress? Nope.

“Mate” and “love” as pronouns. Never sounds right when said by Americans.

"This list is incomplete so sling your hook you slapper!". /s

Wouldn't mind being able to call someone who's being a jackass a 'plonker', but I think in an American accent it would sound like some kind of obscure slur

NOT chuffed? that's a load of bollocks.

I don't mind wheeliebin. We have a tendency to naff-ify everyday items so they always sound unglamourous - witness Brit garage "garidge" vs US "gararj"). In Australia they were called "Otto", after the company that made them. 

Not sure which words I'm uncomfortable with. 

I try not to use Twat even though it can still happen when I'm really exasperated. 

Also loo and bog for toilet I avoid. Only bog is really off limits though.