This is a horrible prank that crossed a big line. You never mess with somebody's food, especially in a racial context like this...and you definitely don't use the term "mutt".
The general rule of thumb when it comes to pranks is that both parties need to laugh at the end of it and that nobody gets hurt...earlier in the episode there was a prank where some officers made it look like somebody smashed this officer's car window only to reveal that the window was actually rolled down...both laughed, nothing was damaged, all around good time. Then this guy ruins it with the dog food.
Hadley crossed the line when he put dog food into Peter Mills' food because of a joke that was put on him when he was a candidate is inexcusable. Good that Hadley never got to make all of Firehouse 51 pay for him being sent out of that firehouse.
To anyone wondering what happened next, Hadley started fires targeting firehouse 51. One fire burning a little girl while Hadley just stood by and watched as it all happened. He was even confronted about it by Severide. Later Hadley was caught and was about to blowup a city street using chemicals with all firefighters in a building but ended up lighting himself and suffering severe burns across his body and was arrested at the hospital. You reap what you sow as the old saying goes.
Wish Hadley took a lesson from this and learned, he’s lucky he didn’t even lose his job and he just got transferred to another firehouse, sure the new firehouse may have been nothing like 51 but still he could’ve taken the opportunity to start over and kept working hard there to move up above the ranks, but yes him getting booted from 51 is on him, him turning to vengeance and playing firebug is on him too which got him burnt and landed him in prison….
In season 2 in the episode “ A nuisance call” how does Hadley start his fires in that warehouse with that Styrofoam white cup and that powder on the bottom of the cup?