Nine is generally against clothes. They're a nuisance. But, during the winter, and when used for this purpose, they are acceptable.
The glasses are a bit of an inside joke. Dice only needs them for reading, but Nine finds them really sexy, so Dice putting on his glasses has become their code for 'nookie now.'

Nine's pants are gonna fall off in three seconds and Dice is lucky his boyfriend is six and a half feet tall or he'd be on his ass in the same amount of time 8|