Comment by Viliam1234

> using un-introduced abbreviations (bonus points for abbreviations that have common meanings, e.g.: EG, NB, IE, ETC)

Every company should give their new employees a list of in-company invented words and abbreviations, so that you don't search for them online and then feel like an idiot for not being able to find them. Especially when the older employees use them as if they are common knowledge.