The episode is (to borrow Robin's most annoying thing) literally entitled Spoiler Alert. And that's all I'm gonna say. Because if you already know what's the most annoying thing about the other four characters, I'd be spoiling it for you.
But, ahhh, I'm also a tease (har!har!)....so click on this video if you haven't seen the episode and you're dying to find out what those annoyances are:
And speaking of annoying...sorry but the voice over on this video is one! Ugh.
[How I Met Your Mother]