You and Spencer never got along. The reason why he doesn’t like you is because you were equally as smart as him..and he hated the fact that he had competition. After arresting an unsub on a now closed case, both you and Spencer had fallen asleep in the backseat of the SUV.

This gave Hotch and Morgan the idea to put all of this unnecessary competition into his own hands. So, he grabbed a pair of handcuffs and puts one around your wrist and the other one around Spencer’s without you both knowing.