Personal space is one of the most invisible cultural settings, and mismatches feel personal even though they are purely cultural. Broadly, northern Europe, North America, and East Asia keep larger conversational distances and touch less, while southern Europe, Latin America, the Middle East, and South Asia stand closer and touch more between friends, and neither side is being rude, just running different defaults. Crowded-country norms add another layer: physical crush on a metro in a dense Asian city carries zero social meaning, while the same proximity on an empty platform would be strange anywhere.
Touch rules have sharper edges than distance rules. Same-gender friends walking hand in hand or arm in arm is normal and non-romantic in parts of South Asia, the Middle East, and Africa, which surprises Western visitors. Cross-gender touch, including handshakes, is avoided in conservative religious communities, so let the other person offer first. Touching anyone's head is offensive in Buddhist cultures, and public romantic affection ranges from unremarkable to genuinely illegal depending on the country, worth checking before couples travel.
The working method never changes: observe the baseline in the first day, mirror it, keep hands to yourself with strangers everywhere, and read withdrawal as information rather than insult. Locals extend enormous grace to visitors who are visibly calibrating.