[Phanx]

I'd do something like this:

local alert = "%s is hogging the %s! (%d)"

local foods = {
	[126503] = true, -- Banquet of the Brew
	[126504] = true, -- Great Banquet of the Brew
	[126492] = true, -- Banquet of the Grill
	[126494] = true, -- Great Banquet of the Grill
	[126501] = true, -- Banquet of the Oven
	[126502] = true, -- Great Banquet of the Oven
	[126497] = true, -- Banquet of the Pot
	[126498] = true, -- Great Banquet of the Pot
	[126499] = true, -- Banquet of the Steamer
	[126500] = true, -- Great Banquet of the Steamer
	[126595] = true, -- Banquet of the Wok
	[126596] = true, -- Great Banquet of the Wok
	[104958] = true, -- Pandaren Banquet
	[105193] = true, -- Great Pandaren Banquet
}

local counts = {}
local endTimes = {}

local started = 0

local f = CreateFrame("Frame", "FoodHog", UIParent)
f:RegisterEvent("UNIT_SPELLCAST_SUCCEEDED")
f:SetScript("OnEvent", function(self, event, unit, spellName, _, _, spellID)
	if event == "UNIT_SPELLCAST_SUCCEEDED" then
		if foods[spellID] then
			started = GetTime()
			self:RegisterEvent("UNIT_AURA")
			print("|cff33ff99FoodHog:|r Monitoring", spellName)
		end
	else
		if GetTime() - started > 180 then
			return self:UnregisterEvent("UNIT_AURA")
		end
		local _, _, _, _, _, _, endTime = UnitAura(unit, "Food")
		if endTime then
			local name, server = UnitName(unit)
			if server and server ~= "" then
				name = name.."-"..server
			end
			local t = endTimes[name]
			if t and t ~= endTime and endTime - t < 20 then
				counts[name] = 1 + (counts[name] or 0)
				if counts[name] > 2 then
					print("|cff33ff99FoodHog:|r", format(alert, name, counts[name]))
				end
			end
			endTimes[name] = endTime
		end
	end
end)

UNIT_SPELLCAST_SUCCEEDED fires a lot less often that COMBAT_LOG_EVENT_UNFILTERED, and gives you the same info for your purposes, so you should use that.

Currently it doesn't track different banquets separately, so if someone clicks multiple banquets repeatedly, it will warn about them, but this seems fine.