Using Inappropriate Words
10-5-2018 | IslamWeb
Question:
Salam. 1. Is it permissible to say "What the heck"?2. Is it permissible to say "Dang" and "Dang it"?3. Is it permissible to say "Darn" and "Darn it"?
Answer:
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad 
is His slave and Messenger.
These words have been changed from the words damn and hell by changing some of the letters, but they are used in the same context and purpose when insulting, cursing and being discontent.
If this is the case, then it is not permissible to utter them because using forbidden insult and curse terms, and being discontent of Allah’s Decree, is not permissible regardless of the words used which lead to it [to this meaning].
Islamic Sharee’ah forbade using lawful words that people use in what is forbidden, and thus the words that are used for cursing, insulting and to reflect discontent [of Allah’s Decree] are more deserving of being prohibited. Allah Says (what means): {O you who have believed, say not [to Allah's Messenger], “Raa’ina” but say, “Unthurna” and listen. And for the disbelievers is a painful punishment.} [Quran 2:104]
Shaykh As-Si'di 
said in his Tafseer of this verse:
“The Muslims used to say when they addressed the Prophet when learning the matters of the religion “Raa’ina”, i.e.: take into consideration our circumstances; they intended a true meaning by saying this word. However, the Jews used to intend a corrupt meaning when using it, so they (the Jews) took advantage of this and started to address the Prophet with it while intending the corrupt meaning. Thereby, Allah forbade the believers from saying this word to close this door.
This confirms that what is permissible can become prohibited if it leads to what is forbidden. It also confirms that one must be well mannered and use words that only hold a good meaning, not to be obscene, and to avoid bad words or words that are confusing or may have an inappropriate meaning. Allah ordered the Muslims to use a word that can only mean something good....” [End of quote]
Allah knows best.