Stars mock Shia LaBeouf's bonkers 'Just do it!' motivational video

Actor Shia LaBeouf.

James Franco has put a potty-mouthed spin on an intense 30-minute motivational speech given by Shia LaBeouf that's gone viral.

LaBeouf gave a pep talk to London fine art students where he agressively yelled "Just do it!" while flexing his muscles in front of a green screen.

"Don't let your dreams be dreams," LaBeouf said. "Yesterday, you said tomorrow - so just do it. Make your dreams come true."

Watch the full 30-minute performance below:

#INTRODUCTIONS from Rönkkö & Turner on Vimeo.

The bizarre rant has inspired plenty of internet parodies, and on Wednesday Hollywood star James Franco jumped on board.

In a video uploaded to Youtube, Franco mimics LaBeouf's speech delivery but changes the phrase from "Just do it" to "Just poo it".

In the clip, the Pineapple Express actor expresses his frustration that children are not toilet-trained.

"Do you want to keep pooping in your little diapers? Just poop in the toilet!" he says.

Another parody inserts LaBeouf's speech into the latest Avengers movie.

This one makes him the centre of an infomercial.

And this Star Wars parody turned him into a hologramed and inserted him into the film.

LaBeouf, the star of the Transformers movie, is known for his peculiar art performances, having walked a red carpet with a paper bag over his head and live-streamed his own heartbeat.

And Franco is no stranger to defending these antics, penning an op-ed column for the New York Times in 2014 expressing empathy for LaBeouf's "erratic behaviour".

- AAP