I personally think I sound like a tool...
Oh I don't mean in general but when I use British words for the sake of conversation or the person I am talking too. So I don't because I don't want to be a tool aka douchebag...
British person (BP): ohh I don't know if I can cut my fringe...
ME: I could never have bangs again because they take to long to grow out!
That is a prime example. Now if I would have said fringe it would be fake and awkward. That would make me a tool.
I feel you should only use words that come naturally, if you have to think, it sounds bad.
I do say knackered but that's natural as I use normally now but never fringe or petrol.
So be true to yourself or you are a tool aka douche.