Who thought of all places that is where he and Hermione would have gotten together? Who would have thought Hermione would ever be in there at all?
McGonagall had trusted Hermione to keep him in line while she was gone. Oh how wrong she was. All he had to do was make her laugh and with the absence of anyone else in the room she had kissed him. Quite a lot. Not that he had complained of course, she was quite good at it.
Now, five years later, Fred looked back happily on his memory of the best detention ever.