Tee via Out of Print Clothing, cardigan and pencil skirt via J. Crew 
Who says you can’t wear a t-shirt and look pulled together? I love one under a cardigan or even with a suit. The key is that the rest of your look needs to be turned up.  Make sure there are no suggestive phrases or rips and holes before you try this style, and evaluate your workplace before you rock one on your 9 to 5. This may not fly in a more conservative environment.