The United States contains multiple daily practices which Americans consider customary but which people from different cultures find offensive because they interpret these practices as showing disrespect. The behaviors which you observe do not constitute incorrect actions because they represent American cultural practices which people from other countries find difficult to understand.
Talking Loudly in Public Places

People in the United States talk on their phones and with their friends at high volume. People in many countries expect public spaces to remain silent. People who speak loudly create an environment that makes others nearby feel their presence.
Smiling at Strangers for No Reason

People in America use smiles to show their friendly attitude. Smiling causes confusion about a person’s true intentions in other cultures. Some cultures reserve smiles for people they actually know.
Calling People by Their First Name

Americans often use first names right away, even with elders or bosses. The practice of using first names to address others in different cultures shows disrespect because it disregards established social hierarchies and age distinctions.
Eating While Walking

The United States sees people eating their food while they walk through the streets. Other countries require people to eat their meals at designated dining locations. People who eat their food while walking create an impression of eating in two different ways which includes eating in a disorderly manner and needing to leave quickly.
Asking Personal Questions Too Soon

American social interactions start with discussions about work and income and personal relationships and age. People from many cultures keep these particular subjects private until they establish trust with others.
Interrupting During Conversations

People in the United States use interruptions to demonstrate their interest in what others say. People from different cultures consider interruptions to be an act of disrespect. People who wait their turn to speak demonstrate both respect and proper social behavior.
Using Phones During Meals

Americans at meal times frequently check their phone devices which they keep on the table. Many places consider this practice to be disrespectful toward the people you eat with.
Expecting Quick Service Everywhere

Americans expect their food service to arrive within a short time frame because this practice has become standard in their culture. People in different cultures view dining as a communal activity which should proceed at a slow pace. People who expedite service operations at restaurants display their entitlement to receive immediate assistance.
Casual Dress in Formal Settings

Americans usually wear informal clothing for their professional jobs and public activities. The custom shows that people from different cultures treat events as less important when they appear in their regular clothing.
Oversharing Opinions

Americans receive encouragement to express their thoughts without restraint. The act of sharing strong political or religious beliefs creates hostile situations in some cultures according to their social norms.
Tipping Culture Confusion

Americans display a tendency to tip their service providers while they expect tips to be given in all situations. Some countries consider tipping of service workers to be disrespectful because they believe that employers should provide necessary service without additional payment.