If you're familiar with Apple's Show Subject feature on an iPhone, you may or may not hate it. It basically makes your text messages look like emails — bolded subject line and all. But if you're not feeling it, there's a simple way to turn it off. Just go to your phone's Settings, hit Messages, hit Show Subject Field, and toggle it to the left so it's off (it'll be white/grey if it's disabled). To make sure it worked, go into iMessages, tap on the pen-and-paper icon in the upper right-hand corner to compose a new text, and the option for Subject Line and Text Body should not appear.
The feature is good if you want to stay organised with your text messages or make a text to a friend or coworker stand out more. So if you have a change of heart, you can easily get it back. All you need to do is go back into Settings, tap Messages, and scroll down once again to Show Subject Field. Toggle it to the right and voila! You'll be sending text with subject lines in no time.