I have nothing against anyone expressing themselves through their clothing, tattoos, etc. but, there's a time and place for everything and on the job site is not always the best place to express yourself.

I had a summer helper a few years back (not quite an apprentice).
He showed up on a new industrial job wearing his pants around his knees so we could all tell what color his boxers were.
This job was alot of underground and alot of climbing steel and ladder work.
I told him politely that he might want to re-think his clothing on a construction site and wear appropriately "fitting" pants for safety's sake if nothing else.
My words fell on deaf ears so, the fourth day, I made that poor sucker climb up and down the ladder as many times as I could just to prove my point. Every time that kid had to start climbing, he had to pull those pants up.
By the fifth day, he showed up in new jeans that fit and wore a fitting pair for the rest of the job.
If you're gonna express yourself, atleast do it in a place where it doesn't have a negative effect on the days work.