In most cases, it's unethical. A best friend relationship is based on trust, mutual respect, and non - sexual affection. Once sexual activities like a blowjob are involved, it can change the dynamic completely. For example, if one person has different expectations afterwards, it can create a rift. Also, it may make other friends uncomfortable if they find out, and can even lead to the breakdown of the friendship group.
If such a situation has occurred, communication is key. Both parties need to be honest about their feelings. They should decide whether they want to try and salvage the friendship or if it's best to part ways. It's important to respect each other's decision.
I don't have such personal experiences to share. But generally, in appropriate stories, good communication and mutual respect between partners often lead to great experiences in relationships.