How sarcastic? Plenty. First the character Jacques is himself sarcastic, ironic, comic, and a receptacle and dispenser of wit, (often sarcastic, as is modern parody) through whom Shakespeare expresses his own jaundiced view of man. Secondly, this reduction of Man to seven stereotypes is reductive, even prejudicial. Thirdly, the language is the opposite of flattering, and the opposite of fair—“mewling and puking”—is that a non-sarcastic view of infants? Just because Shakespeare is a keen observer of the human condition does not mean he is kind-hearted or even sympathetic. All retired persons note the truth of
“The lean and slipper'd pantaloon,
With spectacles on nose, and pouch on side,
His youthful hose well sav'd, a world too wide,
For his shrunk shank, and his big manly voice,
Turning again towards childish treble, pipes
And whistles in his sound”, but no-one is flattered by it.
At the last age he again uses pitiless detail to give a portrait:
“ Last scene of all,
That ends this strange eventful history,
Is second childishness and mere oblivion,
Sans teeth, sans eyes, sans taste, sans everything.”
Sarcasm can, however, be imbedded in the character who utters it (here, Jacques), without entirely faulting the author. We must look at other characters that Shakespeare staged (Lear, Coriolanus, Troilus, for example) to find the full range of Shakespeare’s view of humanity. Jacques stands in for Renaissance or Elizabethan persons of London who did in fact take this sarcastic view of humanity, who felt they were “above” the common man. In that respect, Shakespeare is being sarcastic in depicting that short-sighted, unflattering view that some real persons carry with them.