The thorn(bush) in this guy or gals’ hand could be a real hindrance. Good use of both hands was essential for the average Israelite to accomplish their essential daily chores in antiquity.
And, while such a thorny experience could be an epiphany for this person, chances are it won’t. In fact, far more likely is the possibility of an even great problem later on – infection!
But the message here is simple. A drunkard will already be impaired from using his or her hand effectively and the thorn only makes matters worse – for the present and in the future.
This situation is then contrasted with “a proverb in the mouth of a fool.”
The drunkard’s hand will be pretty useless in doing the good things that need to be done. So an insightful word (“proverb”) in a fool’s mouth will accomplish very little good.
While the message might be appropriate, the messenger’s manner of life will consistently get in the way. Sort of reminds me of a modern wise saying – “Your actions speak so loudly that I can’t hear a word you’re saying!”