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The disparaging slang expression short-arse designates a person of small stature.

This expression occurs, for example, in the following from The Bubble Wrap Boy (London: Penguin Books Ltd, 2014), by the British author Phil Earle (born 1974) [chapter 1, page 2]:

Good things come in small packages.
[…]
Have you ever heard a twee‑er, glibber, more patronizing sentence in your life?
What does it mean? It has no substance, no sub‑text, nothing.
All it is is a gargantuan, ironic pat on the head from people who really want to tell you that your life as a short‑arse is going to be packed with woe and anguish.

These are, in chronological order, the earliest occurrences of the expression short-arse that I have found:
—Note: These early occurrences are all from bilingual (English-French and French-English) dictionaries by the Swiss lexicographer Guy Miege (1644-1718?):

1-: From A New Dictionary French and English, With Another English and French; According to the Present Use, and Modern Orthography of the French. Inrich’d With New Words, Choice Phrases, and Apposite Proverbs; Digested Into a most Accurate Method; And Contrived For the Use both of English and Foreiners (London: Printed by Tho. Dawks, for Thomas Basset, 1677) [s.v. Short, sig. Xx2, column 3]:

A short man (or by derision) a short-arse, un petit homme.

2-: From A Dictionary of Barbarous French. Or, A Collection, By way of Alphabet, of Obsolete, Provincial, Mis-spelt, and Made Words in French. Taken out of Cotgrave’s Dictionary With some Additions. A Work much desired, and now performed, For the Satisfaction of such as Read Old French (London: Printed by J. C. for Thomas Basset, 1679) [s.v. CO, page unnumbered, column 3]:

Courtes-fesses, a short-arse.

—Note: The definition of the obsolete French expression courtes-fesses (which here translates as small buttocks) is as follows in A Dictionarie of the French and English Tongues (London: Printed by Adam Islip, 1611), by the English lexicographer Randle Cotgrave [s.v. Court (adjective), page unnumbered, column 1]:

Courtes-fesses. A Button-breech ¹; one that is pin-buttockt ²; or hath but small or slender buttocks.

¹ Here, the noun button is used figuratively of something regarded as resembling a button, in being small and rounded; and the singular noun breech designates the part of the body covered by this garment, i.e., the buttocks.
² The adjective pin-buttocked means: having narrow or bony buttocks.

3-: From A Short Dictionary English and French, With another French and English. According to the present Use, And modern Orthography (London: Printed for Thomas Basset, 1684) [s.v. Arse, sig. D2, column 1]:

A short-Arse, or little man, un petit homme.

4 to 8-: From The Great French Dictionary. In Two Parts. The First, French and English. The Second, English and French; According to the Ancient and Modern Orthography. [&c.] (London: Printed by J. Redmayne, for Tho. Bassett, 1688):

4-: [First Part, s.v. Avorton, page unnumbered, column 1]:

As, † ³ quel petit avorton est cela? what little shrimp (what short Arse) is that?

³ Guy Miege explained the signification of the dagger symbol (i.e., †) as follows in the Preface to his dictionary:

† Shews, that the Word is only used in a burlesk, jocose, or comical Sense; or else, that it is not current in any Style, but is either forced, or Provincial, or such as grows out of date.

5-: [First Part, s.v. Bout, page unnumbered, column 2]:

† Elle a epousé un petit bout d’Homme, cd. ⁴ un Pygmée, un petit Homme, she married a short Arse of a Man.

⁴ Guy Miege explained the signification of the abbreviation cd. as follows in the Preface to his dictionary:

cd. stands for c’est à dire, that is to say.

6-: [First Part, s.v. NA, page unnumbered, column 1]:

† Nabot, (m.) Terme de Mepris, a short Arse, a Shrimp, or little Man.
† Nabote, (f.) a short Arse, a little Woman.

7-: [First Part, s.v. RA, page unnumbered, column 2]:

† Ragot, (m.) As, un petit ragot, a little Man, Shrimp, † a short Arse.

8-: [Second Part, s.v. Arse, page unnumbered, column 3]:

A short Arse, un petit Corps, † un petit Avorton.