Source : Webster's Revised Unabridged Dictionary (1913)

Irreverently \Ir*rev"er*ent*ly\, adv.
   In an irreverent manner.

Source : WordNet®

irreverently
     adv 1: without respect; "the student irreverently mimicked the
            teacher in his presence" [ant: {reverentially}]
     2: in an irreverent manner; "in the seventeenth century England
        had known fifty years of doctrinal quarrels and civil war;
        clergymen had been turned from their cures, and churches
        irreverently used"