Depending upon the circumstances prevailing at the time, any act of familiarity may be interpreted in either of two ways.
On the one hand, it may be an expression of friendly companionship, on the other, it may be a deliberate puncturing of pomposity.
One such act of familiarity, very common today, is the bestowal of a nickname. Another, not so common today as at times in the past, is a chuck under the chin.
In Old French, the latter was sous bruchet (modern French would have it sous-brechet; the synonymous term in Italian is sottobecco), “under the throat (beak).”
This came to be applied also to the giving of a nickname, and the two-word phrase became telescoped to the single word sobriquet, in which form it was taken directly into English over three hundred years ago.