Here's a list of an easier understanding of ''how to get a Pokemon to dislike you''.
- Fainting, It will negatively affect your relationship with the Pokemon, of course, but as long as you revive it quickly--or if it has a status ailment, you correct it quickly--the relationship will rebound quickly.
The Pokemon faints in battle. (-1 for all happiness values)
•Use of Energypowder (-5 for values 0-199, -10 for values 200-249)
•Use of Heal Powder (-5 for values 0-199, -10 for values 200-249)
•Use of Energy Root (-10 for values 0-199, -15 for values 200-249)
•Use of Revival Herb (-15 for values 0-199, -20 for values 200-249)
•As mentioned before, trading your Pokemon will reset its happiness to its base value, so be warned.
how to:- Best started as a lv 1 Pokemon (ideally ev trained first) Reason, explaining later.. Once ev's are done and your Pokemons lv is low. Fight stronger Pokemon than it and everytime it gets a status condition, use heal powder -5 value >dislike<, use energy root -10 and so on... Reason for ev train first - Once you do get a Pokemon to dislike you. Place it in the pc straight away to keep it's like/dislike status.
Take the Pokemon to the happiness checker which is located at Laverre city (Within the Pokémon Fan Club in Laverre City, there is this girl who will look at the Pokémon in the front of your party. She will tell you how happy it is with various statements. This can be done any number of times throughout the day.)
Source:- Revised info from all sorts of site (wiki, google and serebii.net) including personal exp. e.g. fainting paragraph.
Hope I helped!