Customs/TSA/INS: surprisingly pleasant. No beady stares. No grilling. Some actual smiling and humour on both sides of the Atlantic.
On the English end of things: "and who do you work for, sir?" "Amazon" "Amazon, eh? I've given them quite a bit of my money!" *laughs*.
On the American end: "what's your tshirt say?" "I'm not Johnny Ramone
" "Who's Johnny Ramone?" *pause* "Uh... a famous American musician. Punk music." "I'll have to ask my son about him, he's into punk" Smiles, chuckles, says "welcome back" and corrects himself to say "enjoy your stay" instead.
I will say that there's something about the way an American says "sir", or perhaps the way it sounds with an American accent that makes it seem more of a challenge than a politeness, however. A caution that this person is not
your friend, and therefore you should act accordingly, rather than an air of respect. Maybe that's just me, though.