Better: "As a thorn which is lifted up in the hand of the drunkard" etc. As such a weapon so used may do mischief to the man himself or to others, so may the sharp, keen-edged proverb when used by one who does not understand it.

[As] a thorn goeth (e) up into the hand of a drunkard, so [is] a parable in the mouth of fools.
(e) By which he hurts both himself and others.

As a thorn goeth up into the hand of a drunkard,.... And he perceives it not; or being in his hand he makes an ill use of it, and hurts himself and others with it;
so is a parable in the mouth of fools, a proverbial sentence respecting religious matters; or a passage of holy Scripture which either he understands not, and has no spiritual perception of, any more than the drunkard has of the thorn in his hand; or which being used as a pun, or by way of jest, as it is the manner of some to pun upon or jest with the Scripture, hurts himself and others, wounds his own conscience, and ruins the souls of others; for it is dangerous meddling with edge tools, and hard to kick against the pricks; so to do is like a drunken man's handling thorns, which he does without judgment, and to his own prejudice and others. Gussetius (x) understands this of a fish hook coming up into the hand of a drunkard empty, without taking any thing by it, and so alike useless is what is said by a fool.
(x) Ebr. Comment. p. 244.

As vexatious and unmanageable as a thorn in a drunkard's hand is a parable to a fool. He will be as apt to misuse is as to use it rightly.

9 A thorn goeth into the hand of a drunkard,
And a proverb in a fool's mouth;
i.e., if a proverb falls into a fool's mouth, it is as if a thorn entered into the hand of a drunken man; the one is as dangerous as the other, for fools misuse such a proverb, which, rightly used, instructs and improves, only to the wounding and grieving of another, as a drunken man makes use of the pointed instrument which he has possession of for coarse raillery, and as a welcome weapon of his strife. The lxx, Syr. (Targ.?), and Jerome interpret עלה in the sense of shooting up, i.e., of growing; Bttcher also, after Proverbs 24:31 and other passages, insists that the thorn which has shot up may be one that has not grown to perfection, and therefore not dangerous. But thorns grow not in the hand of any one; and one also does not perceive why the poet should speak of it as growing in the hand of a drunken man, which the use of the hand with it would only make worse. We have here עלה בידי, i.e., it has come into my hand, commonly used in the Mishna, which is used where anything, according to intention, falls into one's hands, as well as where it comes accidentally and unsought for, e.g., Nazir 23a, מי שׁנתכוון לעלות בידו בשׂר חזיר ועלה בידו בשׂר טלה, he who designs to obtain swine's flesh and (accidentally) obtains lamb's flesh. Thus rightly Heidenheim, Lwenstein, and the Venet.: ἄκανθα ἀνέβη εἰς χεῖρα μεθύοντος. חוח signifies a thorn bush, 2-Kings 14:9,
(Note: The plur. חוחים, 1-Samuel 13:6, signifies not thorn bushes, but rock-splitting; in Damascus, chôcha means a little gate in the wing of a large door; vid., Wetstein's Nordarabien, p. 23.)
as well as a thorn, Song 2:2, but where not the thorns of the rose, and indeed no rose at all, is meant. Luther thinks of the rose with the thorn when he explains: "When a drunkard carries and brandishes in his hand a thorn bush, he scratches more with it than allows the roses to be smelled - so a fool with the Scriptures, or a right saying, often does more harm than good." This paraphrase of Luther's interprets עלה ביד more correctly than his translation does; on the other hand, the latter more correctly is satisfied with a thorn twig (as a thorn twig which pierces into the hand of a drunken man); the roses are, however, assumed contrary to the text. This holds good also against Wessely's explanation: "the Mashal is like a rose not without thorns, but in the mouth of a fool is like a thorn without a rose, as when a drunken man seeks to pluck roses and gains by his effort nothing but being pierced by thorns." The idea of roses is to be rejected, because at the time when this proverb was formed there were no roses in Palestine. The proverb certainly means that a right Mashal, i.e., an ingenious excellent maxim, is something more and better than a חוח (the prick as of the Jewish thorn, Zizyphus vulgaris, or the Christus-thorn, the Ziz spina Christi); but in the mouth of a fool such a maxim becomes only a useless and a hurtful thing; for the fool so makes use of it, that he only embarrasses others and recklessly does injury to them. The lxx translates משׁל by δουλεία, and the Aram. by שׁטיוּתא; how the latter reached this "folly" is not apparent; but the lxx vocalized משׁל, according to which Hitzig, at the same time changing שׁכּור into שׂכוּר, translates: "thorns shoot up by the hand of the hireling, and tyranny by the mouth of fools." Although a hired labourer, yet, on this account, he is not devoid of conscience; thus 9a so corrected has something in its favour: one ought, as far as possible, to do all with his own hand; but the thought in 9b is far-fetched, and if Hitzig explains that want of judgment in the state councils creates despotism, so, on the other hand, Proverbs 24:7 says that the fool cannot give counsel in the gate, and therefore he holds his mouth.

A thorn - As a thorn is in a drunkard's hand, which he cannot manage cautiously, but employs to his own and others hurt. So - As unprofitable, and, by accident, hurtful to himself and others.