Assuming we’re talking about Classic:
Pure stunlock build is generally going to be a hemo build. It usually looks like 21, 3, 27. These numbers can vary somewhat, if someone wants to take a bit more in assassination over subtly for unknown reasons.
The important talents are basically going to be dirty tricks, hemo, improved gouge, and initiative.
Initiative means you have a 75% chance of getting 3 CP on the opener. This means that you can cheapshot > double hemo (total of 110 energy), and then slide into a 5 point kidney (total of 135 energy used; you regen 40 energy during the 40 second cheapshot stun).
Improved gouge is used incase you don’t get that initiative proc. It allows you to go cheapshot > hemo > gouge > regen > 4 point kidney.
After you’re in the kidney, they’ll generally be able to build up 3 combo points, pop CB, and get a crit that will finish off just about any non plate user. There might be a 0.5 to 1.00 second ‘opening’ at the end of the kidney, depending on where they were in their energy regen cycle when they opened on you.
This is also assuming no 5 point nightslayer, which results in a super clean stunlock.
It’s important to realize that this build is absolute garbage in pve. Rogues who are running hemo are 100% in it for the pvp, and are being carried to gear in their raids unless they’re respecing. Not much of a problem in MC, but just saying.
If you want to try and do a clean stunlock without being hemo, your best bet is probably going to be SF daggers. 31/8/12 to be precise. That, with 5 piece nightslayer, gives you two options:
The high-risk, high upfront burst combo. CS > backstab > kidney > backstab. This has about a 50% chance of having 4 CP when you kidney, due to the backstab crit, and should let you get one more backstab off at the very end of the kidney. This will kill undergeared players, and leave decently geared clothies (without hots / shields already on them) at critical levels by the time they’re unstunned. On the flipside, it’ll also leave you at 0 energy with an unstunned enemy at the end… Allowing them to hard cast a heal / CC you, unless you have grenades.
The low upfront-burst combo: Cheapshot > SS > imp gouge > kidney. This combo will let you pull off a 100% stunlock for a longer period of time, but leaves you more vulnerable to other enemies showing up and screwing up your 1v1. It is, however, more reliable and less dependent on RNG. Where as the CS > Backstab combo has the potential to leave you at 3 CP on your kidney, this combo will always have you at 4 CP for the kidney. In addition it has a good chance (double whatever your crit % is, so generally just around 50%) chance to allow you to land the kidney at 5 points; because either SS or Gouge critting will give you the extra combo points you need. Watching your energy ticks will result in you being able to backstab very quickly after the kidney lands (you should be at 0.5 seconds before you regen to 60 energy when you cast the KS on the breaking gouge). If you proc Relentless Strikes you can land a backstab right after the kidney GCD, and another within about 1 seconds of the kidney expiration. You can reliably do this; you’ll have a 80% chance to proc the 25 energy regen with no crits, but then you add on the chance to crit with SS and gouge, so real numbers are more like 90% of the time you’ll be able to squeeze out 2 backstabs in that time frame. If you pick up improved kidney shot (+9% damage to targets in kidney), this is the highest burst you can do without losing control. While this combo is slightly more RNG dependent than hemo’s combo, and offers the chance for help to arrive.
The above combo, the low-upfront-burst, is also the best use for thistle tea. You will wind up with exactly 0 energy right after you KS > backstab with it. This means you can pop a tea, pump out two more backstabs, and then a cold blood eviscerate before the target escapes your stun. This is the combo most people are thinking about when they talk about vanilla rogues “stunning you to death”. It’s our kill combo.
EDIT: This is, of course, build variety in this. The SF daggers build I’m talking about invests points into Improved Ambush. I personally do 30/8/13 because I can flex into 5 piece nightslayer, because sometimes our utility in pvp is the ability to delete someone even without stuns; and nothing says “Hello healers” like a 75% chance to turn your opening ambush into a 1600 nuke, and then follow up with a 1200 backstab. However, you can just as viably put those 2-3 points (depending on if you need vigor or not to do the combo right) into initiative. This removes the guess work from getting 5 cp in the CS phase of the combo, and makes it so you can transition from gouge into a 5 point kidney more than 80-85% of the time. So it’s more reliable for duels and 1-on-1 situations, but (imo) less useful for multi-enemy situations because you won’t be able to reliably remove one target from the fight with a non-stun opener.