Is it;
"Of course you're lying."
Or;
"Of course, you're lying."
Gut says the first is right and the second nonsensical but, of course, one's gut can make some odd choices and I just noticed myself undetmining my argument in this sentence.
Of course, now I find myself writing the one I thought incorrect by choice, so...
Self-contradictory of Hammersmith (Of course I'm lying - I'm in Dublin) [There; done it by my first choice and I still like it.]