A gentleman in a green coat smoking and drinking in an interior, with a sprig of oak in his hat

It is likely that the figure in this painting is celebrating the Royal Oak Day holiday (29th May). It became customary to decorate hats and clothing with sprigs of oak during this holiday. Traditionally, it commemorated the return of Charles II to the throne after exile in 1660. It is said he hid from Cromwell's forces after the defeat at the Battle of Worcester in 1651 in an oak tree. The King instigated the holiday on his return to the throne.