There are plenty of other tricks that can be used and won't break the "triple click". I just threw together [1] as an example (and in that one, even if you don't triple click but accidentally select past the end of the line, you are also getting unexpected text).

Combine a few of those techniques with a fancy-looking text box that you are supposed to "click to copy" to get a command, and it becomes pretty easy to even write css-only "exploits" to put stuff in the clipboard!

[1] https://jsfiddle.net/gxosfn83/1/