What does the Bible mean by "those that urinate against the wall" in I Samuel 25:22?
There are different translations for the phrase; what is the Hebrew, what does it really mean?
The Hebrew is משתין בקיר, mashtin b'kir. Mashtin is used frequently in the Talmud for "urinate", and kir is wall. So David is saying "there won't be left alive even one thing-that-urinates-against-the-wall."
The classical commentaries say that means either a male human being, or a dog. Either way, it was intended as a disparaging reference.
Many English translators, either out of puritanism or for clarity and brevity, translate simply "a man."
See here for another case of translators being squeamish about urination.
Targum Jonathan consistently translates this phrase (it also appears a few times in I and II Kings) as ידע מדע, "one who knows knowledge." Rashi explains that he gets this from the Hebrew by taking משתין as related to משית, "arranges" or "sets," so that it can be translated as "one who arranges [his thoughts] in the walls of his heart" - i.e., an adult with intelligence. (According to that, then, it might well include both men and women.)
It is still possible that it's actually a double entendre - meant, as Shalom pointed out, to sound disparaging - while also having another, less obvious, meaning.
We pondered this phrase when learning Nach, and came away eventually that it is a disparaging term for men.
With the understanding that men and women are different in so many ways beyond the physical and that these differences are appropriate and desirable, the men referred in this way have nothing but sheer anatomy to distinguish them from women.
If you are sexist and think that men are better than women (as I imagine the men of that time were), then it would be insulting to describe a man as a woman.
Memory fails me, but I think this idea comes from one of the commentators and is not original.
Hesiod, in Works and Days, tells men where not to urinate (standing turned toward the sun, on the road or off the road walking) and says "the godly man of sound sense does it squatting or going to the wall of the courtyard enclosure." M. L. West, Trans. Perhaps the passage in question refers to godly men.