That is when you try to kill everyone you see, find interesting ways to do it, like summon (PC console commands) the weakest creature you can find a code for, and see how many of them it takes to kill guards of various factions.
Or go to a town and summon one beastie and give it 15k or 20k hit points and see if it can kill everyone.
Find your own interesting thing to do, I personally enjoy using no clip to go up in the air, summon someone or something to me and see if it survives the fall, then find out at what height they will die if I go up just a little farther, but not at the current height I am at.
Next on my list is to make a bow that shoots faster than any other in the game and does not do any damage (already have a mod with "practice arrows" that do no damage) and play around with various poisons and enchants. Once I get that down good, I intend to make a new character that is only allowed to use the bow of no damage with practice arrows, and see how boring/hard the game is. I have a feeling I'll be using a lot of paralyze effects... Would be interesting to see how much I can do in game without ever causing 1 point of damage (dragons may have to be excluded, or I might just skip the main quest line... Probably get bored after a couple dozen hours anyway)
Also you could install Skywind and help out with developing that. I've been inactive on there for about 40 days, might go get some more work done on that. Will be nice to play morrowind with the skyrim engine.