Enter Pipa Middleton, the younger sister of Kate Middleton. Never has there been a rear-end obsession like that attached to Pippa Middleton, as a nation begins to prepare Ass Appreciation Day in honour of the royal relative's rump.

Consumers of the British media may as well consider the younger Middleton sister as the one who married Prince William in April, as Pippa - who turns 28 today- steals headlines from sibling Catherine, the Duchess of Cambridge and wife of Prince William. We do wonder if Catherine feels sad or glad? Probably a nice break from the spotlight though.

Since the brunette walked down the aisle of Westminster Abbey behind her sister, hangers on have apparently been left in a blinding daze by the sight of her petite-slim figure, in particular her derriere.

Several social networking sites have profiles dedicated to this woman's bottom, some boasting hundreds of thousands of followers.

"Hey, even I - a straight woman - can appreciate female perfection when I see it!" writes one follower on the Facebook profile/group: Pippa Middleton ass appreciation day.

The public event is scheduled for September 9 at 11.30pm (0930 AEST Sept 10) until 2.30am (1230 AEST Sept 10) the following day.

And the venue? ... "Prince Harry's bedroom."

By way of explanation, the cheeky event is "A day when Pippa's ass will join the greatest in the buttocks hall of fame alongside (Hollywood actors) Jessica Alba and Angelina Jolie".

English literature graduate Pippa, who dates successful London financier and cricketer Alex Loudon, appears in British newspapers almost daily, always happy and smiling, seemingly unfazed by the craze she has stirred. That'd be right.

The paparazzi followed her on a recent holiday to Spain with friends and in May the snappers were quick to capture the moment she flashed some of Pippa's coveted backside while climbing into a car juggling her bag, a takeaway coffee and keys, reminiscent of a circus act possibly.

Mobs of lenses hang around her dark-coloured convertible BMW Z4 and last week the whole of the UK knew when a parking ticket was slapped on its windscreen - a sheepish Pippa left to retrieve her fine under the close eye of a country's cameramen.

Unconfirmed reports say that such is the concern of millionaire parents Michael and Carole Middleton, they are considering ordering a STG100,000 ($A153,490) bomb-proof BMW or Audi for Pippa to drive.

Going by comments that have been shared on Pippa fan sites, a strengthening of security might be in order.

While we are on the topic of such an auspicious day as Ass Appreciation Day, it may be a helpful catalyst for more fun and colourful celebration days to come. Endowment Enchantment Day? Boobs Are My Breast Friends Day? The potential is limitless. See if you can come up with some. Definitely a laugh. Or perhaps the writer is jealous his derriere is not receiving the same level of attention...