Laudator Temporis Acti

Camillo P. Merlino, "Some Old French Words in Current English," in Herbert H. Golden, ed., Studies in Honor of Samuel Montefiore Waxman (Boston: Boston University Press, 1969), pp. 56-65 (at 61):

LAMPOON. Clearly derived from lampons, first-person plural of the Old French lamper, a nasal formation from the Anglo-Saxon lapian, "to lap up, to guzzle," lampoon came to mean a drinking song; it is from the refrain lampons "let's drink," frequently recurring in ribald and satirical songs. From this background emerges our familiar lampoon in all its connotations. In modern French there still remains the popular lampée (f.) grande gorgée de liquide qu'on hume d'un coup, such as une lampée de vin. But lampons, strangely enough, has fallen by the wayside.

The first thing that sets off my bullshit detector is the claim that an Old French word is derived from an Anglo-Saxon word. Unlikely. See Calvert Watkins, The American Heritage Dictionary Indo-European Roots (Boston: Houghton Mifflin Company, 1985), p. 34:

lab-. Lapping, smacking the lips; to lick. Variant of leb-². 1. Germanic *lapjan in Old English lapian, to lap up: LAP². 2. Nasalized form *la-m-b- in: a. Germanic *lamp- in French lamper, to gulp down: LAMPOON; b. Latin lambere, to lick: LAMBENT. [Pok. lab- 651.]

Second, I'm not sure what is meant by the assertion that "lampons ... has fallen by the wayside." As a verb it survives as a toast: see e.g. Richard Olney, Lulu's Provençal Table (London: Grub Street, 2013), page number unknown:

The animated discussions at table turn around the food, the wines, and their relations to one another. As euphoria gains ground, Lucien may ask everyone to stand while he solemnly intones the ritual toast to "notre chère Méduse," figurehead of the Provençal wine confraternity, after which all present drain their glasses ("Lampons!") and exclaim "Alléluia! Alléluia!"

On the etymology of lampoon, see Leo Spitzer, "Anglo-French Etymologies," Studies in Philology 41.4 (October, 1944) 521-543 (at 525-527).