Nicole Richie is no stranger to bad behaviour - she was once one of Hollywood's most notorious party girls - but yesterday she was upstaged by a rather naughty animal.

The star was forced to make a swift exit from an exclusive boutique on Melrose Avenue after an anti-social dog cocked its leg up an expensive purple dress.

She had earlier been enjoying a shopping spree ahead of a birthday party for rocker boyfriend Joel Madden, who turns 29 today.

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VIP: Nicole Richie shops in an Melrose Avenue boutique, but she was joined by a rather anti-social customer

No puppy love: a little dog leaves an unwanted surprise on an expensive dress during Nicole's visit

She was spotted visiting a party supplies store where she picked out a 'Pushing 30' birthday card and decorations including balloons and a 12 foot party banner.

It has been a time of celebration for the couple - they recently welcomed their first child Harlow Winter.

Nicole's father singer Lionel Richie, who refers to himself as 'G-Pa', can't stop gushing about the new addition to their family.

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It's time to go: the star wrapped up the shopping spree before making a swift exit

He added that Nicole "has turned into a fully-fledged mom. It's the most frightening thing in the world because you keep thinking, 'Are you going out?' And [she's like], 'No, dad, can't go out! She has another feeding - I have to be right here!'"

However she is expected to take a night off from her motherhood duties this Friday to join Joel for the opening of DCMA Collective, a clothing store he is opening with his brother Benji.

Nicole's friend and Simple Life co-star Paris Hilton is also expected to attend - she has been dating Good Charlotte rocker Benji for almost a month.