You will be coaxed into a host bar by many boys, you will order a drink and all the boys will disappear! Happens all the time. However if interested, you can call a boy to sit with you and no problem. Sometimes boys will sit with you, uninvited, and you can buy them a drink or say "not interested". If a boy does sit with you and you buy him a drink, it is still expected to give him a tip such as 100 Baht. If you are a regular, and known to have a boys sit with you, then they will not forget and will approach you for a drink and conversation. If interested in a boy, just off him, or make arrangements to see him at a later time/date.