A shirt is a shirt. It's still YOUR shirt - its not like its a uniform or something. Its a shirt. I think you need to really understand that the shirt has absolutely no barring either way. Go shopping and try on different professional shirts. If someone shows up to a (lawyer's) interview or any interview at all wearing a tshirt, that's not very professional. Considering other people who interview for the same job will be wearing suits and ties. It may come across as you not caring a lot about getting the job and being "too casual" which subconsciously makes people feel like you wouldn't take the job seriously. Have you considered pairing the tshirt with a nice professional vest? Again, realize that its just a shirt, it doesn't have control or power over you, you're the one creating these little barriers in your way, not the shirt.