This cartoon by Andy Davey from The Sun combines three stories: David Cameron's controversial comments about Pakistan's record on combating terrorism, Pakistan's president Asif Ali Zardari's meeting with Cameron later this week, and the current cricket Test Match series between England and Pakistan.
A bouncer in the sport of cricket is defined by Wikipedia as "a type of delivery, usually bowled by a fast bowler. It is pitched short so that it bounces on the pitch well short of the batsman and rears up to chest or head height (or even higher) as it reaches the batsman." In the figurative sense, if someone bowls you a bouncer, they ask you a tricky question, which is exactly what Zardari is likely to do when he meets Cameron.
Being an integral part of life in many nations which used to be part of the British Empire, cricket has lent many metaphors to the English language. This page attempts to explain cricketing metaphors and how they derive from actual usage in cricket.