The big diff between a T-shirt and shirt is their design, material, and purpose:

T-shirt usually rocks a chill design with short sleeves, round neck, and no collar. It’s all about that soft, stretchy cotton vibe.

Shirt: Typically refers to a button-down or button-up shirt, which has a collar, a front placket with buttons, and often long sleeves. It is usually made from woven fabrics like cotton, linen, or polyester blends.

Material: 

T-shirt: Made from knit fabrics that are flexible and comfortable. The material tends to be lighter and more casual.

Shirt: Crafted from fancy woven fabrics for that extra crisp and formal vibe.

Purpose: 

T-shirt: Donned for chill vibes, perfect for daily shenanigans or as a layering piece. It might rock funky prints and cool designs.

Shirt: Sometimes seen strutting its stuff in fancy places like the office or swanky shindigs. It's got range - can go classy with a suit or chillax in a casual vibe, depending on the groove.

T-shirts are the chill cousin, perfect for laid-back vibes, while shirts are the uptight sibling, suited for serious occasions.