A proper men's muscle tee — the kind that's actually cut for shoulders, not the kind that looks like you took scissors to a regular tee at 1am.
Deep scoop, short sleeves, body skims clean. Wear it to the gym, wear it under a jacket, wear it on its own when the weather's good.
100% long-staple cotton — soft on day one, still soft on wash fifty. The kind of basic you reach for first and replace last.
Classic black. Three sizes. Easy.