Several formal occasions necessitate a man wearing a boutonnière. Any man involved in a wedding usually wears at least a small boutonnière attached to his left lapel. Young men attending formal proms also wear a boutonnière on the lapel of their tuxedos. If you look carefully at the left lapel of a suit coat or tuxedo jacket, you will notice a buttonhole. This buttonhole is the location where you attach the boutonnière. Put on a boutonnière with a buttonhole to attach the flowers to the man's lapel.
Position the boutonnière onto the man's left lapel so the base of the flower(s) is even with the buttonhole. Do not insert the floral stems through the buttonhole---they rest over the buttonhole. Make the stems of the boutonnière extend below the buttonhole.
Hold the boutonnière in place with one hand and adjust the angle of the boutonnière to ensure it looks attractive on the lapel. Position the floral pin behind the lapel.
Insert the floral pin up through the lapel from behind just under the buttonhole. Immediately insert the pin completely through the floral stem of the boutonnière and then poke the pin back down through the lapel fabric.
Check the boutonnière after pinning to ensure it looks satisfactory. Adjust the angle of the boutonnière slightly, if necessary, by rotating it gently on the lapel. You should be able to perform small adjustments after pinning; but if the boutonnière is significantly askew, you will have to pin it again.