Inigo's innocent veneer has been stripped away. Bucky had siblings back home, he knows exactly what he's in for, now that he's gotten over the shock (and the awe!) of Inigo being the one to level this sort of tit-for-tat at him.

His smug grin is the only warning Inigo gets before Bucky takes aim with his next bit of information. "I've done more than just smell him," why does that have to sound so weird??? "I've kissed him. Several times." Just today, even. In fact, today was the first kiss. "I'm one hundred years old, not dead," to quote an old friend of his.