“Let me be mad, then, by all means! mad with the madness of Absinthe, the wildest, most luxurious madness in the world! Vive la folie! Vive l'amour! Vive l'animalisme! Vive le Diable!”

Variant: We're all mad here.
Source: Alice in Wonderland

Ran (1985)
Variant: In a mad world, only the mad are sane.

Mellow Yellow (1966)

Shameless
Song lyrics

Cogito and The History of Madness, p.37 (Routledge classics edition)
Writing and Difference (1978)

Yea and Nay : A series of lectures and counter-lectures given at the London school of economics in aid of the hospitals of London (1923) edited by C David Stelling, Section IV, Poetry and Modern Poetry
Context: Let us speak of our madness. We are always being called mad. If we are mad — we and our brothers in America who are walking hand in hand with us in the vanguard of progress — at least we are mad in company with most of our great predecessors and all the most intelligent foreigners. Beethoven, Schumann, and Wagner, Shelley, Blake, Keats, Coleridge, Wordsworth were all mad in turn. We shall be proud to join them in the Asylum to which they are now consigned.

Source: The Eyre Affair

Source: Inferno