When you tell your line manager what you've got to work on for the day... and they assume it's going to fill up your entire day.
I'm never sure whether to flag their over-estimation of the workload, or ponder if I'm missing something obvious.
Then end up doing the "well, should I flag up I've got bugger all work to do unless emergency things pop up in the inbox or just lurk and feel mildly fraudulent?"