While his demeanour may have screamed 'new to this' once he actually got to drinking it would be easy to mistake Castiel for an old pro – one with slightly awkward habits, granted, but definitely not someone taking their first ever shot of whiskey. It might have amounted to a different, altogether milder sort of heresy, failing to pause and appreciate either the colour or the scent, but Ruby's directions had been to drain the glass and drain it Cas did, tipping the shot into his mouth and letting it sit there for a moment while he set the tumbler back down, his expression a mix of placid and curious as if expecting some miraculous effect.
It didn't burn exactly, though it prickled at the base of his tongue, and when he swallowed it was a warm, heavy weight sliding down his throat, past his lungs, towards his stomach. The experience was... different. He would reserve judgement on whether or not it was enjoyable per se.
“And humans do this for fun” - Cas' I really don't understand those creatures half-frown returned as he glanced over at Ruby.
That was the drinking part of the plan covered, at least; the bartender had already started refilling. Which only left the talking, which would no doubt be somewhat further from painless. What did people talk about while drinking? The notion of 'smalltalk' was still fairly foreign, but “You've been to Ireland before.” (statement, more than question) was a safe opening gambit.