is it easy for a British or an Australian guy to understand American slang ? or vice versa ?
for example, can you understand what Joe said in the follow conversation without the translation.

Joe Cool: This is like a totally rad company. Man, it's phat. like rippin'. I can for sure supersize in a total ten place like this, sir.
(Translation: This is a great company. It's impressive. Very impressive. I can really make a contribution to a great company like this one, sir.)

Interviewer: Well,Mr Cool, thank you for your time. I shall waste no time reading your resume.

Joe Cool: Slap me five.
(translation: You're insulting me.)

Question

is it easy for a British or an Australian guy to understand American slang ? or vice versa ?
for example, can you understand what Joe said in the follow conversation without the translation.

Joe Cool: This is like a totally rad company. Man, it's phat. like rippin'. I can for sure supersize in a total ten place like this, sir.
(Translation: This is a great company. It's impressive. Very impressive. I can really make a contribution to a great company like this one, sir.)
 
Interviewer: Well,Mr Cool, thank you for your time. I shall waste no time reading your resume.

Joe Cool: Slap me five.
(translation: You're insulting me.)

Answer

I think its easy to understand slang from other countried from the context, just hearing someone saying something I should be able to understand what theyre trying to say and learn the slang. Also American TV shows are very common everywhere in the world so their slang is known everywhere. Australian may be slightly more difficult to understand.

Theres a lot of English slang that transcends borders though.

Answer

I believe it is, because slang is used on internet and has thus crossed the borders of all countries. The same has happened in Spanish-speaking countries, one notable example being the adoption by the mexicans of the term 'huevon' from the Chileans, only adapted to their own slang in the form of 'pinche huevon' - a hybrid. Sorry, I won't translate, even under torture! A similar case is an Australian saying something like 'bloody wicked pair o' wheels you got there, mate!', referring to a motorcycle that s/he liked.