brown-nosing, ha ha? like always telling someone 'that's a great idea boss, let's do that'?.. lol

This is a difficult question to answer. Could you please give some extra context because my best guess is that we would use phrases such as: sucking up to over solicitous fawning (verb) It was painful to watch Trevor fawning over Angela at the party. Hope this helps.

A sycophant is always trying to praise someone because he wants something in return. A sychopant is around someone = is sucking up to someone = is brown-nosing (these are slang terms)

If someone was always around another person in that situation I would say they were trailing, following along, or stalking the other person.

Do you mean psychopath?