” if i show up to shul in jeans and a t-shirt i should be able to join a minyan like a regular guy. “
Though I totally do not think that mode of dress is the BEST way to show up in Shul, I had this experience with my son who tried very hard never to miss a minyan. He was going from a camp job and did not have the time to change, or he would have missed the minyan which was an open to the public daily minyan at a local Yeshivah. He was in jeans and a casual shirt, and when he came into the shul was immediastely asked to leave by someone choshuv in the Yeshivah. Had he not been my son and were he not firmly committed to his Yiddishkeit, this humiliating action could have been the straw that broke the camel’s back in turning him off the derech. And the person responsible would have been smug in his not allowing “someone like that” inside HIS shul. Mind you, I had a long talk with him about the inadvisability of going into shul straight from camp before having a chance to change, but I commended him for making the minyan a priority, no matter what.