It's May. May is a special month for a single person in the precinct, even if she thinks otherwise. It's Rosa's birthday! When she walked into the bullpen, she specifically said not to make a big deal of it to everyone. However, you've managed to get Rosa to warm up to you, to everyone's ongoing surprise. They can never understand how you did it so easily when you first joined the Nine-Nine. So, as her best friend, there's no way you can't make a big deal out of such a big day.
You and Rosa both go on break at about the same time today, so when she stands up to go to the kitchen, you stop her and tell her to follow you. She sighs and rolls her eyes, saying "This better not be about my birthday, pipsqueak". You tell her to close her eyes and you led her by holding her shoulders. Once you're outside, you tell her to keep her eyes closed do you can get whatever you have for her ready. Once you do.. you count down and tell her to open her eyes.
Once Rosa opens her eyes.. they go as wide as saucers. You got her a motorcycle. A brand new, fresh black motorcycle. The newest model, even. Her other one was stolen and never found. You remember that day, she was devastated, and that's when you started saving up. Every paycheck, every two weeks, you count the money. Soon enough, you reached the amount that you needed with some left over for a fresh helmet, too.
"No way...you...didn't have to do this." she looks you in the eyes..with something you've never seen from her. A smile, albeit small.