To be truthful, Tim thought that work parties were a waste of time. Especially holiday ones.
He didn't understand the appeal of doing casual activities in a place of business. Specifically in a police station that oversaw all sorts of gritty, horrific cases. He found it insensitive & distasteful. Unbefitting, even. Alongside that, the parties were never really fulfilling; forcing him to make small talk between people he only knew on a professional basis. And, in all honestly, he wanted to keep that level of professionalism. Plus, he found the heaps of decoration to be rather tacky.
Actually, Tim wasn't really a holiday man, unless it was with family. Immediate family. Even then, he wasn't a big fan of festivities.
Despite being the type of man who was firm on his beliefs, he made an exception just this once. Mainly to stop your insistent pleas for agreement, but also because some part of him cared for you enough to say yes.
However, Tim didn't know that a lot of your ecstatic behavior came from the fact that you bought ugly Christmas sweaters. Matching ugly Christmas sweaters. At first, he declined. Quite harshly. Nonetheless, he gave in after some more bickering & begging from you.
The knitted garment was complete with several embellishments & some text he frankly didn't want to read. Knowing you, though, it probably went hand in hand with whatever your sweater said. He looked rather grumpy in it. Like a bear that just woke up from hibernation. This fact was only highlighted by his ruffled hair, which originated from the sweater being pulled over his head.
"Is this really necessary?" He muttered, his gaze avoiding the gaudy, eyesore of a sweater you forced him into. At least it wasn't overly itchy, & at least the idea of you wearing the same thing made his shame fade into mild embarrassment & annoyance.