1. In the very first town, you can help rustle a retard's cattle and cause him to be yelled at by his mother so that he runs away into a canyon and is trapped by a psycho robot. If you don't rescue him, it can be reliably said that he dies of starvation or worse.
2. You can straight up shoot said rustlers in the face in their shop and no one would blink an eye (close the door first or it gets messy fast).
3. In the Den (second town, usually), you can become a slaver and sell your companion(s) into slavery, join slave raids and the like.
4. Similar to the first town, you can outright shoot both shopkeepers in the face in the Den and no one blinks an eye. In fact, one of them gives positive karma when offed.
5. You can betray Lara and her gang by informing Tyler that she is going to raid the church, resulting in her running straight into an ambush.
6. In Redding, you can supply a prostitute with drugs and she eventually ODs.
7. In Madoc, you can have sex with both brother and sister, get into a shotgun wedding, sell your spouse into slavery or prostitution, come back and tell the father (who forced you into the shotgun wedding) and he dies of a heart attack from the news. Getting said spouse killed or killing him/her yourself also works.
8. Cause a nuclear reactor to meltdown, and consequently having to kill a bunch of ghouls in Gecko if you just follow the main quest and do as the racist bitch asked. Find the third option.
9. Blow up a mine at the behest of racists and kill most of the supermutants in Broken Hill.
10. Tear up Curtis' doll in front of him for the giggles.
11. Assassinate two different people at the behest of Bishop. In fact, just assassinations in general in New Reno. Everyone wants to kill everyone there.
12. Murder the innocent deathclaw in Navarro at the behest of the Nazi scientist. And if you don't kill the scientist, he sends his report and results in everyone, deathclaw or otherwise, in Vault 13 getting massacred (RP patch fixes the bug so that killing the scientist stops that from happening).
13. Getting that little shit Myron to follow you, send him down the hole in Golgotha where Pretty Boy Llyod has his stash, and covering up the grave. Yup, you just buried the little bastard alive. Congrats. You gained 100000000 karma.
The list goes on and on and on.