As of 2008 there were approximately 17000 ATPL/CPL holders in the UK.
With a population of 61 million, you would have to meet 3588 people before you were statistically likely to meet an airline pilot.
Assuming that 20% of the 17000 are unemployed then your chances of meeting an unemployed airline pilot are one in 17941.
I'm sure you realise I was joking, but for the sake of arguement you're not taking into account the likely demographic of those I meet. Very few of the one third of the 61 million population that are under 16 or over retirement age will have an ATPL for example
, and I assure you they don't make up much of a proportion of those I meet.
The people I do meet: those studying a maths/science/engineering course at uni like me, or those who frequent the airfields I fly at, however, I'm sure you'll agree are much more likely candidates.