“My shrug was so nonchalant it would make a cat jealous”

Source: Grip of the Shadow Plague

Source: Every Day

Beaumont and Fletcher Philaster, Act III, sc. ii, line 144.
These lines are used almost unaltered ("holds" becoming "does hold") in Act III, sc. ii of Buckingham's The Restauration, an adaptation of Philaster. They appear with an attribution to Buckingham in many 19th century collections of quotations, e.g. Henry George Bohn A Dictionary of Quotations from the English Poets (1867) p. 63, and hence also on several quotation websites.
Misattributed

Rhinoceros (1959)

"My Old Cat", as given in The Nation's Favourite Twentieth Century Poems, pub. BBC, 1999

"Sisters of Mercy"
Songs of Leonard Cohen (1967)
Context: When I left they were sleeping, I hope you run into them soon.
Don't turn on the lights, you can read their address by the moon.
And you won't make me jealous if I hear that they sweetened your night:
We weren't lovers like that and besides it would still be all right.

Variant: I hate my body. I like so many other people's bodies. I like legs — a good pair of legs on someone else always makes me jealous.
Source: "Is Kate turning into Keira?" by Clemmie Moodie The Standard (1 December 2005) https://www.standard.co.uk/showbiz/is-kate-turning-into-keira-7250578.html
Source: Celebrity W.T.F’s Volume 107(16 December 2005) https://lindagallacher.blogspot.com/2005/12/celebrity-wtfs-volume-107.html

A Tramp Abroad (1880)
Context: You may say a cat uses good grammar. Well, a cat does -- but you let a cat get excited once; you let a cat get to pulling fur with another cat on a shed, nights, and you'll hear grammar that will give you the lockjaw. Ignorant people think it's the noise which fighting cats make that is so aggravating, but it ain't so; it's the sickening grammar they use.

Source: Notebook