Severus had been on the receiving end of many nefarious pranks in his life. They were particularly prominent during April Fool's Day. Albus always encouraged teachers to allow students to play tricks – after all, it was harmless and just for one day.
Severus always said you'd have to be a bloody fool to play a trick on him.
Unfortunately for him, Gryffindors were just that: bloody fools.
And so every year, he was the lucky recipient of nasty pranks. All done ostensibly in the spirit of the day, but with 364 days of hatred behind it.
The long list of pranks played on him ran all the way back to his school days. That stupid Shrieking Shack incident hadn't been the only trick those idiot Marauders played on him. They'd played many others, all of them nasty, all of them humiliating.
Mind you, Severus had given as good as he got. He had never been one to sit back and allow others to humiliate him.
So the Marauders, after their tricks, suddenly found their potions exploding, their homework gone, their friends alienating them without reason…
And ever since he started teaching, Gryffindors foolish enough to play tricks on him found themselves spending months in detention doing the filthiest work Severus could come up with. And he was extremely inventive.
His friends (yes, he had friends) enjoyed playing tricks on him too. He couldn't get back at them, not as satisfyingly, anyway.
And there was no way to get back at Albus, who had more nefarious pranks up his sleeve than anyone else.
He had learned to become wary of any secrecy. Especially when it was utterly uncalled for.
So when Harry started making firecalls and cut the connection anytime Severus walked in the room, hid correspondence from him, and was often gone for no reason for long periods of time, Severus was apprehensive.
And worried.
Was Harry just planning a particularly complex (and nasty) trick, or was he seeing someone else? He couldn't really believe his Harry would do that, but… He would not be the first jilted lover.
"You see…" Harry's voice from the sitting room wafted towards him through the open door. Severus headed closer.
No more was forthcoming. Harry had cut the connection suddenly. "Hi, love," he greeted, kissing Severus chastely. "How are you?"
Severus smiled wanly. "I am fine, thank you." He wouldn't ask Harry about the secrecy.
And this went on for days.
Until one day. He walked into their rooms to find them in total darkness. Harry was always in by now, and the lights were always on. In any case, Harry usually left a torch burning so that they wouldn't bump into something.
"Lumos," Severus said softly, forcing tears back. Apparently, Harry had… left.
"SURPRISE!!"
People starting jumping out from behind the couch, the armchair, out of cabinets, behind doors… Oh. A surprise party. Hence the secrecy.
"Happy birthday, Sev," Harry laughed, kissing him.
The least nefarious plan possible, Severus grinned to himself.
Nefarious – adj. Wicked in the extreme; iniquitous. ('s Word of the Day, March 18, 2008)