#1 - Harry or Severus are very self-conscious about their body (for whatever reason - could be anything from knobbly knees to a super big dick).
#2 - AU! Harry owns a pet shop and Sveerus comes by, because he doesn't have a clue how to take care of his friend Minerva McGonagall's cat (Minerva is on holiday or sth).
#3 - A crazy wozard captures Harry and Severus and puts them into a dungeon. They have to fight through the maze-like halls to find each other.
...*coughs*...
#4 - Harry discovers D&D for himself (maybe Neville and George play too?) and keeps it a secret from Severus, because he doesn't want Severus to think he's a nerd.
#5 - AU! Severus has a flower shop and Harry comes by to buy flowers. Of course Severus thinks he might be buying them for a date, when really Harry only busy them for Mrs Weasley... Misunderstandings and botched attempts at flirting ensue!