Unlike most countries, the tipping system works rather differently in Bangladesh. Poverty is an issue in the country, and therefore most people do not expect tips. Tipping a hairdresser or taxi driver is definitely not customary. Sometimes however, waiters and waitresses at restaurants may be tipped. This however is very unexpected and is considered as an ostentatious display of gratitude. There is definitely no fixed rate for tipping, however, anything between 2 - 10% is advisable.
Etiquette and mannerism is quite different from the western world. Bumping on someone is duly apologised not merely by pronouncing 'sorry' as in the west but also along with body language and surely with more wordings like 'Extremely sorry! Didn't see. Please excuse for this time.' or words to that effect. Thanking a retail clerk for her services is not generally in practice. However, doing so is not considered wrong although do not expect a response like "your welcome" if you do so. Population is an issue in the country, so personal space may disappear in most public places such as banks or stores. So if someone gets too close to you, he or she is not being inappropriate.
But on the whole, life goes on in the country and do not let the general lack of etiquette (Western Style) stop you from experiencing the countries major sights and attractions.
If you visit the rural Bangladesh then you might experience a different type of hospitality. People are amiable, friendly and extend their helping hands even if you don't expect. If you have a keen eye then definitely you will find Bangladeshi version of Etiquette and Manner. English is widely understood although not all of them can speak.