The book, שערי תשובה, written by Rabbeinu Yona, discusses the subject of speech. Generally, this falls under the category of a לאו שאין בו מעשה, a prohibition not accompanied by an action, but there are some exceptions.
Saying words of Torah in front of an immodestly dressed person, or when one is naked himself, is forbidden.
It falls under the category of והיה מחניך קדוש, that one must keep his camp holy.
Similarly, one must not speak דברי תורה where there is a bad odor, or in a dirty alley.
There are other types of speech where one could be subject to lashes. If one swears falsely, or curses his friend using Hashem’s holy name, are severe transgressions. In such situations, this is a חילול ה׳, the desecration of the name of G-d.
One should not make unnecessary oaths, as an additional negative commandment. And finally, one should not use speech to curse a Jewish leader, or any Jew, for that matter.
In short, we need to heed Rabbeinu Yona, and be extremely careful with our speech.