Right in the Jewels is a Killzone HD trophy exclusive to Rico.
This trophy is earned by playing as Rico, on any level or difficulty. Walking up to the nearest helghast and pressing the melee button. Using the M224-A3 in melle will result in Rico thrusting the gun into the Groin of a helghast. Doing so 20 times will unlock this trophy.
It doesn't matter how often you do the melee kill or where. All that needs to happen is that the melee animation must play out for the kill to count.