Taken from Gamefaqs:
http://www.gamefaqs.com/boards/959557-fallout-new-vegas/56913080

Please keep this bumped. Maybe we can cut down on the billion topics about this that pop up every day.

Here's the step-by-step guide to get the NCR Ranger Combat Armor as painlessly and with as little consequences as possible:

1. Go to The Strip to meet Mr House. This can be done fairly early in the game.
2. Leave the building after meeting him, and a guy will tell you to go to the south end of the strip to the NCR building.
3. Talk to the NCR ambassador.
4. Do a series of quests
5. Once finished the quest involving the Kings sends you to Hoover Dam to acquire more missions, go to Camp Forlorn Hope.
6. Go up to one of the sniper towers
7. Start pushing the NCR Veteran down the ramp while pressing A over and over to keep talking to him so that he doesn't start walking away
8. Push him off the cliff, still pressing A again and again to keep him from running off
9. Shoot him in the head a couple times while sneaking
10. Profit.

Note: About 75% of the time this will make it so you do not gain infamy!

Enjoy your armor!
^__^

Ps. Special thanks to SkunkySkunk for figuring out a way to get the Vet away from the camp!

Think i'll just try and get the armor the hard way?

But nice find!

Put Bomb in Pocket Bro!

I think the tactic is to avoid getting attacked by other NCR members.

Where this is a glitch and you either push the npc out of the ncr area or you push them off a ledge and they die. Hence not giving you bad karma or vilifying you.

Thats what you has a stelf boi on!

I'm gonna guess it still negatively affects their attitude towards you Stelf boi or not. No one witnesses you killing cobbs small gang yet instantly your vilified by the powder gangers!

Hmm...DISGUISE!

oooh the possibilities.

I got that armor easily by doing the "We are Legion" side quest.

If you really really really want to get the armor without risking any penalty, clear your cache and use the incendiary ammo glitch offline.