A trophy shag, to sleep with a star or very posh person who is very inaccessible.
You would then tell all your friends and effectly wear the "trophy" around your neck.
Pippa Middleton would be consider posh and inaccessible due to her sisters recent marriage...hence pippa-bling
Friend A get's phone out to show friend a picture of the very posh girl he slept with last night who his friends doubted he'd ever do due to her extreme posh-ness
A: Check out the pippa-bling I got last night!
B: Dude she is well posh....I never thought you'd nail that!