There were a few select things that made Castiel uncomfortable. One of them was people badmouthing his family. That was one kind of uncomfortable.
There were two things that made him the other kind of uncomfortable: Sam Winchester walking around without a shirt, and Sam Winchester speaking Latin. The second kind of uncomfortable was distinctly more pleasurable, and he found himself looking for excuses to experience it.
"Sam, I cannot make out this particular passage. What does it say?" he would ask, cheeks pink. Sam would raise an eyebrow but read it out loud, and Castiel would bite back a groan.
"Sam, I cannot tend that wound while you are completely clothed," he would say sternly. Sam would shrug and pull of his t-shirt, and Castiel would try not to choke a little.
"Sam, we should have sex," he said finally. Sam grinned.
"Took you long enough to ask," he answered, and pulled him close.
"Sam?" Castiel managed, once Sam gave him a moment to breathe.
"Mm?" Sam smirked, chasing Castiel's lips.
"Speak Latin to me," Castiel requested.
"Facta, non verba," Sam murmured, and swallowed Castiel's reply in a kiss.