I watched that Jihadis Next Door programme with my teenage daughter and she said some of her Muslim schoolmates make jokes about ISIS.
The impression I got was that they do it as way to take the piss out of stereotypes - and are quite funny with it.
For example one class was asked to do a flow chart of their career goals after school and one kid wrote:
"Go Syria -> Join Isis -> Blow stuff up"
And showed it to her mates (who fell about laughing at the outrageousness -and implausibility of it) before tearing it up and doing the proper one.
But inevitably it doesn't always work and today some poor kid was grilled about their beliefs and Syria and I think had to bring in their passport to school, parents involved etc. Because of a piss-taking joke.
Obviously these kids are more interested in video games, football, YouTube etc than religion...