First let's define the words. ERRATIC = It means irregular or unpredictable. It can often refer to someone's behaviour... Often when used to refer to behaviour it refers to unpredictable and undesirable behaviour. ECCENTRIC = It just means unconventional or slightly strange. It's quite commonly used as a part-compliment... Erratic, however, is nearly always used negatively. That's a big clue with regards to your questions... --- 1) "arriving late in the morning" = You'd say it was erratic behaviour on most occasions, (it suggests being unpredictable. Of course, if somebody is ALWAYS late it's not erratic. But erratic fits better.). 2) "Working until late in the evening" = It could be either. I would personally go with ERRATIC but, again, it depends on whether or not it's predictable. If someone doesn't always work late then it's erratic. If someone stays late at the office for no reason, however, we could say it's ECCENTRIC. 3) "singing in the office" = We'd say it's eccentric because it's a little "over the top" and unconventional. 4) "appearing distracted or sleepy in meetings" = We'd say it was "erratic" behaviour because it's undesired and, let's assume, unpredictable behaviour. 5) "wearing clothes that don't match" = We'd say that it's ECCENTRIC because it's unconventional and quirky. 6) "missing deadlines" = We'd say that it's ERRATIC because it's undesirable and unpredictable. 7) "drinking ahcohol at lunch" = I think I'd say this is more likely to be ERRATIC. It could still be eccentric but I think erratic fits this better... 8) "being aggressive to subordinates" = Again, I would use ERRATIC. It could be called "eccentric" but usually only if it's done in an at least semi-joking way. --- Please look at my definitions and you will see that ERRATIC or ECCENTRIC could fit nearly all of these sentences. I've matched them as I think they would most COMMONLY be used. -- Good luck and take care!