According to the search results, a boutonniere should be placed on the left lapel of a suit jacket or shirt. Specifically, the largest part of the flower should be placed over the buttonhole on the left lapel, with the base of the flower where the ribbon-covered stem begins laying on the lapel below the buttonhole. The stem of the boutonniere should be aligned with the sides of the lapel so it angles in the same direction. If someone else is pinning the boutonniere on you, it should be placed to the right of the tie.