AHHHHHHH attacked while watching a couple of snarry vids (gobuss, ariel lindt, and gin119 are amazing, you should look at their vids over on Youtube and gobuss/ariel lindt's site
http://arielgobuss.tnb.pl/viewpage.php?page_id=14 ) by this snarry idea:
Okay, so this is either very, very chan (third year) which I'm personally not a huge fan of ( super young chan I mean. I actually quite like 15-18 chan) but don't mind if done right, much later when Harry is the DADA teacher, or some time in between, where Harry is either doing a boggart for the DA (reviewing patronus for new comers?) or helping a teacher with a class.
Harry has been seeing Severus for some amount of time, and either Harry has been secretly harboring insecurities or Severus remains rather IC and keeps up the somewhat mean-spirited snarks, insulting Harry's intelligence etc., although he means it more as teasing than as to hurt Harry (socially awkward!Snape).
Anyway, Harry is expecting his boggart to be a dementor, but low and behold it's a big, bat-ish Snape sneering down at Harry, uttering the choicest, juiciest cannon insults (Mr. Potter...our new celebrity, etc.). This completely shakes Harry, but the students/his friends/if the chan version, Professor Lupin, don't make the connection and just give him a sympathetic pat on the shoulder and commiserate with him about the evilness of the potions master.
Maybe that gets back to Snape later, and confronts Harry about it, or Severus later feels betrayed by Harry (someone kisses Harry and Sev sees, thinking Harry is cheating on him, Harry publishes something in the paper about how Severus is innocent and it pisses Sev off, there relationship is splashed across the front page of the Prophet and Severus gets howlers and is mad/breaks it off with Harry), and Severus unknowingly copies the boggart and Harry has a break down of some sort, either manly or sobbing-teary