Okay, what the...?!

Ugh... Sorry your boss is such a jerk. That is the main reason I dress business M-F. My co-workers laugh at me, but for the reason it happened to you and others I've witness. Saving casual after 5pm Fridays! Hope you feel better!
 
was your shirt loose and not tight like the others? Maybe he was picking on you cuz he cant see your boobs. what a total assmunch. i'm so glad and fortunate that my boss is an amazing people person and is not a total psycho *****.
 
This month's Cosmo has a great item about how to pull off the casual look at the office without looking TOO casual.

(One tip: wear dark wash jeans, because they're easier to dress up.)
 
A peice of advice: he told you this verbally, right? If you can, EMAIL him to "clarify" his policy on t-shirts. Be really innocent about it. Get this person to tell you this in WRITING. Save this email for future use. The reason I say this is that often employers begin building "cases" when they want to let someone go.. and this may be what he's trying to do. Also if you can get the HR person to tell you that t-shirts are OK in an email, get that and save it. Forward the copies to your home computer and save them there.

Call me paranoid but I've seen these tactics before... and the rule of thumb is to cover your @ss. ALWAYS.
 
He should have told you he disliked t-shirts the first time you wore one, not months later and blow up about it! Ridiculous. Unfortunately, the only thing you can do is not wear jeans or t-shirts... I know it's awful to have such a nit-picky boss, but sometimes its best just not to give him a reason to lecture you.
 
Ask him who the t-shirt rule applies to, is it just you or is it for everyone? If he's picking on you, see if he's dumb enough to say it, can't favor or pick on certain employees. What applies to one applies to all-keep notes!
 
Back in the early 80s I worked in the art dept. (photo lab) for Reynolds Metals Co. here in VA. OK--first of all, it was THE 80s. Second, it was AN ART DEPARTMENT. Third--PHOTO LAB. This means a DARKROOM in the BASEMENT. We were all college students except of course for our many bosses. I used to get dragged into the office pretty regularily to be scolded for what I was wearing. I'll never forget the time I wore a pair of (really hot) leopard-skin-print jeans. My supervisor called me in the next day and said, "well, the reviews are rolling in!" You have to remember I'm in Virginia. This company was ultra-conservative, in fact the cafeteria was still segregated unti the mid-70s. It pissed me off at the time but now I think it's funny.

Your boss may have a bit of a letch for you, you know, which would explain why he is singling you out.
 
It's no fun having a policy firmly in place and then having one person come in and think they can change everything on a whim then have a pi$$ing contest with the staff over it!
 
While this is completely obnoxious, I think you should probably just not wear t-shirts anymore (though i would stay with the jeans, and probably do what Roo suggests and get it in writing that you can wear jeans.

While this sounds completely unjust and unfair and ridiculous, keep in mind that your employer can fire you for any reason or no reason at all.