You can blur out text that might be a spoiler and the reader has to just click on it to expose the text.
Click on the blurred text below to learn how (spoiler alert):
When composing a message in the toolbar there is a gear icon. Click on that and chose Blur Spoiler. Text will be added that looks like this:
[spoiler]This text will be blurred[/spoiler]
Then just replace “This text will be blurred” with the text you want blurred and you are done.