This list may be useful:
http://forums.civfanatics.com/showthread.php?t=345910
You know a leader is planning a war because in the diplo. window, if you try to bribe them to declare war on someone, they object with "we have enough on our hands right now" (WHEOOHRN is the forum abbreviation).
About half the leaders in the game will not start planning war against you at Pleased status; anyone not on that list is a pretty safe neighbor. Note that simply because an AI isn't on that list doesn't make them a
totally safe neighbor - that is only the most common way AIs get into wars. If they start planning before you get them to Pleased, getting them there doesn't make them call off the planned war. If you refuse a demand, most AIs have a small chance of immediately planning to attack you. Apostolic Palace resolutions can drag them into wars with you. Some AIs can be bribed to attack at Pleased even though they won't plan such attacks on their own initiative. If you have vassals, your diplo. relations get massively messed with (it's no longer just how they feel about you, it's also how they feel about your vassals, so even someone you are Friendly with might attack you if they hate your vassal).
The supreme backstabber would probably have to be Catherine. She's the only AI in the game who can be bribed to attack someone who is Friendly to her. Beyond that, anyone in the "Sociopathic" category in that list I linked to is a definitely painful neighbor; any of those neighbors should leave you with three options. 1) Cripple or kill them early, or 2) Use bribes to keep them busy warring other people, so they don't attack you. Your last option is 3) Expect to be attacked at the most inconvenient time and place.
If you have "random personalities" turned on in game settings, each AI's name gets matched with a random different AI's personality (e.g., you can have the personality of Ragnar but named Gandhi). That's about the only case in which you're likely to see Gandhi backstab you.
