Aristophanes, Clouds 1329-1330. The lexicographer quotes these two lines in reverse order and without regard to the speakers, who are the befuddled and battered Strepsiades and his sophistic son Pheidippides.
Note that the initial insult is by a father to his son! (The rest is the son's response.) Strictly speaking the insult suggests that the one insulted has been the passive partner in anal intercourse, but in fact -- like "bugger" etc. nowadays -- is more general in application: see J.Henderson, The Maculate Muse (New Haven 1975) 210 #461. For lakkos cf. lambda 58, lambda 60, lambda 61.