The best t-shirt brands for a slim guy are Buck Mason, Asket, and J.Crew. Buck Mason is designed specifically for a slim athletic build with a tailored fit through the chest and arms. Their crew neck tees come in regular and tall sizes to ensure proper slim proportions. Asket also offers a trim slim fit style made of lightweight jersey cotton. J.Crew's broken-in tees feature slim sleeves and a tapered cut. For thin or lanky guys who want that ideal trim but not skintight fit, Buck Mason, Asket and J.Crew provide excellent slim-cut t-shirt options.