Garcia buys her and Reid matching/complimentary outfits. Reid finds it highly amusing.
Every now and then, he and Garcia will coordinate their fits and show up to the office in the same outfit at which point everyone busts up laughing. (Partly because it's always startling to see Reid in anything even half as outlandish as what Garcia usually wears, and partly because of Morgan's reactions every time.)
Garcia does a pretty good job of getting an even number of matching outfits for both her eccentric style and Reid's more neutral one.
And yes, this does mean that Reid sometimes wears dresses, skirts, and high heels.
The first time Garcia and Reid walked into the bullpen wearing matching checkerboard dresses with chess pieces patterned across them (I'm imagining they were custom made and are supposed to reflect a moment in an actual chess match of some sort which Reid was over the moon about bc hes a dork and Garcia knows it) and little black pumps (because Reid wasn't tall enough already) with both of their hair up in half pony tails and matching glasses, Morgan tripped over his own feet and almost ate it right there in the middle of the bullpen because holy shit his Baby Girl and his Pretty Boy are stunning and hold up he needs a minute.
Spencer, walking into the bullpen with Penelope: *info dumping about the chess match modeled on their dresses*
Morgan, getting coffee across the room: *chokes on his own spit and almost drops his mug because he's busy staring at Spence and Penny*
Prentiss, walking up beside him and slapping him on the back as he coughs: lmao real smooth, Derek. *sips at her own coffee*
JJ: *enters the bullpen in a pencil skirt and an off the shoulder blouse, her hair put up in a bun*
Prentiss: *chokes on her coffee, unable to tear her eyes away from JJ*
Derek: lmao real smooth, Emily. *walks away laughing*