If you're familiar with Apple's Show Subject feature on an iPhone [1], you may or may not hate it. It basically makes your text messages [2] 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, find Show Subject Field, and toggle it to the left so it's off (it'll be white/gray 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 organized 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 [3], 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.