Question: Does the Bible condemn calling one a fool?
Answer: Our question suggests the Bible is our standard of determining right and wrong. Indeed, God'' word is the standard (Gal. 2:14).
Calling someone a fool can be wrong. Jesus condemned calling one a fool out of unjustified anger (Matt. 5:22). If one calls another a fool out of sinful hate, then calling someone such a name (or any similar term) is wrong.
Calling someone a fool is not automatically wrong. Our question illustrates the need to taking all the Bible has to say on a given subject before we arrive at a conclusion. Jesus called some fools. Here him: "Ye fools and blind..." (Matt. 23:19). In this same chapter Jesus calls these people "Hypocrites" and "blind guides." Yet, beloved, Jesus was without sin (Heb. 4:15). Jesus was clear in his teaching (in such cases). He clearly identified those against whom he spoke (Matt. 23:2ff).
The Bible often calls certain ones fools (empty headed or refusing to do God's will). The atheist is called a fool (Ps. 14:1), the slanderer is said to be a fool (Prov. 10:18), those who despise instruction (Prov. 15:5), a contentious person (Prov. 18:6), the one who lives for pleasure (Luke 12:13-20), the one who trusts in his won heart (Prov. 28:26) all are called fools by God.
Beloved, Christ called those who do not build on a rock (Christ's teaching), but build on the sand fools (Matt. 7:26, 27). What is your status, in God's sight? Are you a wise person or a foolish individual. You can change your status now, but the Judgement Day will be too late (Heb. 3:7,8).