while i agree with wbrett1027, his explanation was.....lacking. (don't get your panties in a bunch, i'm not trying youuuu)
the auto-ignition temperature of gasoline is ~280*C. That means in perfect conditions
, if gas (liquid or vapor) comes in contact with a surface that is ~280*C, it will ignite.
Real world testing shows auto-ignition temperatures to be several hundred degrees higher.
A typical butane lighter (big) has a flame with reaches 1977*C.
So yes, a lighter will ignite gasoline (liquid or vapor). But as mythbusters proved in an episode, the cigarette itself will not ignite gasoline liquid, but it will ignite the vapors.
SO NO SMOKING AT THE PUMP
*disclaimer* gasoline gives off vapors, which explode, don't try this yourself, just watch mythbusters