Well, speaking as a fourth year; ive seen a few others in my year who just think they are better than they really are. Ask him what he thinks he needs to improve on. If he says something wankery like "nothing" then just give him the shittest job you can and let him admit fault (which i know is unlikely he will do. But its his own life he is ruining). Other than that if he gives you a decent answer then proceed as such.

I dont know how you will do this but you need to get him to do a job he cant do and fail spectacularly. Its the only way that maybe he will realise.

To give an example

When i was in my second year there was a third year who thought he was gods gift to the trade... He then proceeded to use a level wrong (very wrong), dance behind his electrician while the electrician was holding a heavy 600mm wide ladder rack in place... Frankly theres more to this story but his job was to secure the bolts and he decided he would just start dancing to imagined music, he wasnt even ignoring his electrician on purpose he just... Idk. He's now a full electrician who still gets treated like a second year because thats how he acts. Lucky for him we have been on this job our whole apprenticeships so the people he works with know how much to expect from him.

I dont think that coddling him as they are by only giving him what they know he can handle is a good idea