Without missing a beat?

My mate just called me and asked did I want to go out to with him tonight, I didn;t fancy it, as soon as he asked, with out the merest hint of hesitation told him I couldn't as I was in Leicester visiting a mate this weekend.

I've no idea why I said Leicester, I think it's cos they let me down on my accumulator today.

Anyway how easy do you find it to make up crap at the drop of a hat and make it believeable?