The reliable danger zones in most countries: domestic politics, religion, and the nation's historical wounds, especially wars, borders, colonialism, and relations with neighbouring countries. Every country has at least one dispute or trauma that outsiders underestimate, and a casual opinion, or even naming a region or sea by the wrong name, can chill a room. Criticism of monarchies or founding figures is actually illegal in a few countries, which is worth checking through official travel advisories before you go.
Money and family are the culturally split topics. Questions about your salary, rent, or marital status are normal warm curiosity in much of Asia, Africa, and the Middle East, so expect them and answer lightly or deflect with humour, no offence intended or taken. Volunteering the same details in Northern Europe or North America can seem odd or boastful. Personal remarks about weight, appearance, or age are casually made in some cultures and wounding in others.
The safe posture everywhere: ask more than you assert, especially about local history and politics; let locals criticise their own country without you joining in; and never compare the host country unfavourably to your own. Redirect awkward moments toward food, travel, sport, and family pride, which are welcome nearly everywhere.