What is a vest? It is typically referred to as the sleeveless jacket. Lately, I've gotten to wearing vests myself as I find them very suitable - for office and casual wear! Some vests are cropped, others are loose and are worn open.
I like the sweater type of vest that suite my blouse very well for office wear. It is stylish and gives an air of formality - besides showing too much of your chest! Even if you are wearing a casual tee, try a button vest over it and be amazed by how much it may have changed your look!