If you're reading my solution, you either have never played GTA V before the xbox one version came out (like me) or you did not complete rank 100 on the xbox 360 version and are hoping to find a "quick and easy" way on the xbox one version to finish rank 100 off. As far as I know, there is no "quick and easy" way like the methods that were around when the game first released on xbox 360.
If you were looking for a quick and easy way to reach rank 100 by reading this solution, you can already look elsewhere, because I never could find any quick way of doing this achievement.*Rank 100 requires 1,584,350 rp*There is the obvious method: Close this tab and just play the game online normally. If you play the game long enough just playing "normally" (and it could take a LONG time) you will eventually get rank 100 or even rank 1000 if you actually want to max out your rank.
Another method: Put together a dedicated group on here or from your friends list and just play missions. Not all missions are available from the beginning so unless you are playing with someone who is a higher level, you will need to play what is available to you and just keep playing the missions that are easiest/funnest for you. Hard mode gives you extra rp and cash so if you can handle it, put the missions on hard. If you find that you can complete a mission in 2 minutes, then just wait at the end of the mission and let 3 or 4 minutes go by. Rockstar changed how you are rewarded so that if you take 5-6 minutes on a mission, you will get more than you would if you beat it in 2 minutes. There are only a couple of issues with this method. Unless you like playing solo on hard, then you are depending on having partners willing to play at the time you are, or needing to play with randoms. The other issue is that you can't simply find a mission that you like and just hit replay on the mission after you finish, like you can when you play deathmatches or races.
The method I used (still took about 90 hours): Before I continue, I would only recommend this to someone who wants to do some reading, homework, handheld gaming, doing something on a second screen because this method only requires that you play for about a minute, rate the mission, then hit replay, wait, repeat. This can be done solo. Get all other miscellaneous online achievements so you get rp toward rank 100 while doing those. In the start menu, go to online > jobs > host job > rockstar created (or bookmarks after you bookmark it) > races > Criminal Records. If you have a Rockstar social club account, you can also just go this link (it links to their site)
http://rsg.ms/e93832c and hit the "add to game" button to have it added to your bookmarks. If you have played GTA V on 360, then you probably know the "Criminal Records" race well, because this used to be the one of the go-to methods for quickly getting rank 100... Then Rockstar butchered the rp payout for everything.
Host "Criminal Records" and set matchmaking to "closed"; you don't want people ending the race early. Set it to two laps and pick a custom vehicle or rent a super-class vehicle. You have two main options here; you can do two laps at the beginning of the race, but stop just before the finish line of the second lap, then wait until the race timer has hit 4 minutes, then finish the race. You could also let the race start and then wait until about 3 minutes has gone by and then complete both laps (if you will finish before the race timer hits 4 minutes, then stop and let it hit 4 minutes, then finish the race). The reason you need to wait for 4 minutes to go by is because that is when this race reaches its maximum rp payout (the max cash payout is at 8 minutes). Try not to crash during at least one of the laps so you can get 100 extra rp during the lap (the bonus only happens once per race).
If you are just starting out (rank 1-30), this race only gives out about 800 rp for 4 minutes. the rp given out increases by 10 rp per rank and every 4 ranks or so it will increase by 15. If you get the clean lap bonus and rate the race everytime before you vote to restart the race, you will slowly gain rp faster and faster. The only reason I would recommend it is because you only have to drive for a minute per race and then let the controller sit for 3 minutes either at the beginning of the race or just before the finish line. This method will drive you up a wall after a while but if you just do this on the side while you're doing something else, you get to do that and get rp. DO NOT finish the race before 4 minutes is up, but you can go over 10 minutes if needed. 15 minutes of inactivity will boot you from the race so if you plan to go away from the game for 15 minutes a lot, then you need to rubber band your controller. If you completely optimize this method, finishing at the 4 minute marker everytime and having decent loading times, you could probably finish rank 100 faster than I did (it took me about 90 hours). Toward the beginning of your ranks, you can get around 10k rp per hour, but toward the end you can get 17k+ rp per hour. It will not be quick, but you will get there.
Those are the methods I can think of. If you know a currently faster method, then feel free to comment it or create your own solution that you think is better. If you plan to just be looking at your screen the entire time you play this game, I would recommend you playing missions by yourself or with partners/randoms instead of grinding "Criminal Records" because you will be sick of looking at "Criminal Records" after just 2 or 3 races.