If a sociopath with an IQ of 100 -- someone for whom understanding calculus would be an impossibility -- is asked for directions by someone with an IQ of 150, and the sociopath points him in the wrong direction, and the 150 believes him, the sociopath figures that makes him smarter than the 150.
He knows, and the nonsociopath doesn't, ergo, the sociopath is smarter. (This is known as "sport lying.")
This is why sociopaths will lie even when they don't have to: it proves how much smarter they are than their victims.
That's a fun feeling, and one which is easily obtainable if you don't have a conscience.