What do you think it means when people use an ellipsis [...] instead of a period [.] at the end of a sentence?

Depends on whether they use it properly or not. My mum uses them after almost every sentence to make her messages unreadable and to piss me off.

It means you're getting all sneaky and shit.

To William Shatneranize a sentence.

I use them all the time...

Probably incorrectly, but fuck it.

"I am unable to form a proper insult or I am trying quite a bit too hard to be interesting or deep".

God, I fucking hate those three bloody dots.