Disclaimer: I am not J.K. Rowling. I do not own Harry Potter.
Note: The following short one-shot takes place at some point during the 1994-1995 (Goblet of Fire) school year. The scene takes place in the quarters at Hogwarts of Barty Crouch junior, at some point during the latter stages of the year. Barty is convinced that his disguise as 'Alastor Moody' is not going to last much longer, but he has captured Severus Snape, whom he has tied up (disarmed of wand but currently alive and conscious) in one corner. This piece is rated 'T'.
"Sorry about this Snape." the untransformed wizard whom Severus Snape vaguely recognised as the supposedly dead Barty Crouch (junior) said. "Only thanks to you my welcome here and previous disguise are wearing out, so it's only fair really that you help me tidy things up, before I depart. Bottoms up."
And he raised the vial of fizzing purple polyjuice, to which he had so recently added a lock of Severus' Snape's hair, to his lips.
Ten seconds later, Barty was thrashing around, helpless on the floor. Twenty seconds later, he was snoring loudly and totally helpless.
A look of faint derision crossed Severus Snape's face. Really. A wizard with as many OWLS as Barty Crouch (junior) had had ought to have wondered whether something about the greasy nature of Severus' hair might react badly with polyjuice – might in fact react with it and actually turn it into something akin to draught of living death, and happen to be something which Severus regularly worked into his scalp just in case anyone ever tried to dopplegang him like this.
Now: the only question was as to how long it would be before someone happened by the defence professor's quarters to investigate for any reason, and rescued Severus?
Author Notes:
Just a brief little piece of fun, speculating that there could be an intended purpose to Severus Snape having greasy hair.
I fully intend to include this idea again (Severus' hair being treated with something designed to react with polyjuice) in other fanfiction.
Update (10th October, 2016):
With regard to the early reviewer who commented regarding Severus Snape and wandless magic, I would rate canon Alastor Moody as being a wizard at least equal to Severus Snape in magical experience - and I figure that if canon Barty Crouch junior can keep canon Alastor Moody captive for most of a school year, that the same Barty Crouch junior can keep Severus tied up for long enough that Severus has better odds of being 'rescued' by someone else than of having sufficient time to eventually free himself.