Hey Jasper welcome to T21
There are a variety of ways to make someone feel unwell. Diarrhetics and laxatives are easy to get hold of and are very effective especially in an enviroment where it aint too easy to keep going to the loo (and gives you very nasty stomach cramps) and do wear of a lot faster than a week but it does put the message across.
I don't know about any "innocent" methods of making someone feel ill for a longer period of time thought... Food poisoning would do the trick however that can get you into serious trouble (not to mention it is just plain nasty and most likely very much illegal).
Maybe you should have a hunt around your local "joke / fun" shop to see what they have down the line of things like that and maybe you'll find a creative way of getting your own back (marbles that give of blue paint when mixed with water and put them in his shower head?) but I would advice caution as you never know how jokes like that are gonna play out (especially when you mess with people's food / drink) as they might have some medical condition you aren't aware off which could cause some nasty complications and it wouldn't be the first time someone ended up dead due to a prank.
There are a variety of ways to make someone feel unwell. Diarrhetics and laxatives are easy to get hold of and are very effective especially in an enviroment where it aint too easy to keep going to the loo (and gives you very nasty stomach cramps) and do wear of a lot faster than a week but it does put the message across.
I don't know about any "innocent" methods of making someone feel ill for a longer period of time thought... Food poisoning would do the trick however that can get you into serious trouble (not to mention it is just plain nasty and most likely very much illegal).
Maybe you should have a hunt around your local "joke / fun" shop to see what they have down the line of things like that and maybe you'll find a creative way of getting your own back (marbles that give of blue paint when mixed with water and put them in his shower head?) but I would advice caution as you never know how jokes like that are gonna play out (especially when you mess with people's food / drink) as they might have some medical condition you aren't aware off which could cause some nasty complications and it wouldn't be the first time someone ended up dead due to a prank.