Remus saying "Sweet Jesus" nearly all the time to the extent when it simply begins to annoy Sirius.

Books fell on Remus's head: Sweet Jesus!
Chocolate box finished: Sweet Jesus!
Awesome prank gone wrong: Sweet Jesus!
Peter stuck in detention: Sweet Jesus!
James walking headfirst into a tree because he was too distracted by Lily: Sweet Jesus!

*One night in the dorm*
*Remus says Sweet Jesus again*

Sirius: (quite annoyed as he couldn't ignore the fact that whenever Remus said those words he looked more adorable than ever due to which Sirius was having difficulty in concentrating on his book on Animagi) Moony, if you say Sweet Jesus one more time, I swear I'll kiss you to oblivion.

*Five minutes later*

"SWEET JESUS!!!"

Sirius closed the book and walked up to a very confused looking Remus then did precisely what he had threatened to do so.

*Awkward silence in the dorm*

Remus: (blushing red like a beetroot) A-are you okay, Sirius?

Sirius: (smirking) Yeah. Never been better.

Remus: (stuttering) Then wh-what was that for?

Sirius: You were asking for it.

*What Sirius didn't know was that it wasn't Remus who had said Sweet Jesus. He hadn't even spoken since the threat. And it was, in fact, James trying to imitate him.

Sweet Jesus!