Yikes!

Gesture: Thumbs up (pt. 1)

What you think it means: "It's all good!"

What it means in Thailand: A serious side-eye (or similar). Some say it's very offensive, while others contend it's more childish than obscene, like sticking your tongue out. Best just to play it safe and keep your hands in your pockets.

Geez!

Gesture: Thumbs up (pt. 2)

What you think it means: "It's all good!"

What it means in Arabic countries: A thumbs up in any Muslim country pretty much means, loosely translated, that you hope the person you're gesturing at has a very pleasant trip to the proctologist.

Is this true?

Gesture: A "V" sign (with the palm facing inward)

What you think it means: "Peace, man!"

What it means in Great Britain and Australia: The equivalent of giving someone the middle finger, it's now clear why the television show "V" -- both the '80s original and the remake -- never made it Down Under.

If it's palm facing inward in America then that's not the Peace symbol--at least the way I remember it--it was only palm facing outward, which is why it kinda worked in the UK too:

Perhaps here in the USA a palm-inward-two-fingers-up just means table for two to the maitre'd, or two tickets needed by scalpers and late showing attendees...