When it comes to rapping, there are a certain set of rules one must follow. You can't just rhyme willy-nilly. That would be silly. Hip-hop is chock-full of cliches - probably more than any other musical genre - and Eminem has the low-down on what you can and can't say next time you're spitting that freestyle.

Eminem at 'Southpaw' premiereEminem at 'Southpaw' premiere

The 45-year-old Detroit star is one of the finest authorities on rap music out there; he stands next to the likes of 2Pac and Biggie as one of the greatest hip-hop artists that ever lived, so he's learned a thing or two in his time about spitting rhymes.

He and his buddies developed a brief list of 'Hip-Hop Don'ts' which they relayed in an Instagram video this week, throwing out some commonly used rhymes that reveal nothing but the terrible imagination of the person using them. You'd be surprised how often you might come across them. 

'If you have an emergency, it cannot be with an urgency', Eminem insists. 'And if it is with an urgency and you are rushed to emergency surgery, you cannot be burned in third degree.'

On the other hand, he added: 'If it's a second degree burn, you can be rushed to emergency surgery but there can be no urgency.'

On a similar note, he revealed that, 'if you're gonna murder me, it cannot be like you never heard of me', suggesting that instead you 'have to know me'.

Others included 'if you wanna be a pimp... you cannot have a limp' and 'you cannot be a mobster and eat lobster'.

You might not believe that last one but it actually comes up in rap lyrics fairly regularly. Take for instance Digital Underground's 'Underwater Rhymes' ('I rock like a mobster/ Told an MC, 'Yo, you look like a lobster'), Meek Mill's 'Monster' ('The money turned my tuna into lobster/ They want to do me, I maneuver like a mobster') and Nate Dogg & Ludacris' 'Real Pimp' ('Veins poppin' out like shimp, lobster/ A-Town mobster').

As for 'pimp with a limp', that's perhaps even more well-used. Swishahouse's 'I'm A Pimp' ('I'm a pimp, I walk with a limp'), Trick Daddy's 'Pimp' ('A Class A pimp/ And I walk with this gangsta ass limp') and Yung Nation's 'Pimp' ('Im the real deal, I pimp... Make my ass walk with a limp') are just such examples.

More: Eminem responds to Bonnaroo critics

So the bottom line is if you want to be able to freestyle like Eminem, get a bit more creative. Or better yet, leave it to the professionals.