I've pugged in my Peregrine once or twice before just for lulz. Even got a couple of kills. (And I got reported... ) I don't make a habit out of doing that but I honestly don't see the problem if anyone chooses to bring some unconventional ship into a random PvP queue.
But you're ruining everyones fun. The opposing team will just target you and everyones skill and effort will be wasted.
Worst case, the match is over in five minutes and you go on to the next one. And as often as not, the lunatic in the shuttle or Miranda or whatever actually knows what he's doing and is more effective than Mr. Clueless in his shiny new Kumari.
Worst case scenario for you. For everyone else in the match you are the worst case scenario.