They don't have any fun. They stay in hell at their desks solving equations to prove themselves equal with God, while on the side working on equations for all of us, weighing our sins next to God's grace, trying to get us down there, because we are all very late for a meeting. Why can't humans just be on time? They are waiting around up there, most of them for seventy years or so. Why can't humans just be on time?
We do the same sort of thing with our sin. They want us to do the same sort of thing, to become mathematicians, accountants, auditors. When we are in sin, when we give into temptation, we are choosing the boring thing. Sin is boring and it makes you anxious. Sin is extra work, something to think about and take care of on the side, except you don't get paid for it, it's a time sink, and it keeps you from activities like enjoying being alive. Sin is no fun.
Satan has a gigantic desk. He has these big reading glasses that fit behind his horns. They have scratches in them, because every surface in Hell is made out of stones.