Please don't get it into the heads of the spotters that frequent these forums that it's okay to blow the slides with the engines running. If the masters aren't cut in time and they choose the "wrong" doors then it's game over.
I don't think the poster who proposed this scenario was suggesting doing so with a view to initiating an evacuation.
But, given an aircraft that has become potentially unairworthy and a crew who don't appear to give a toss, you can't deny that blowing the slide would be a pretty good way of getting their attention and making sure the aircraft wasn't going anywhere.
What would you have done instead ?