One of the most irritating ones I've experienced is when your character knows instantly how to use a weapon, particularly guns. Now, today's shooters are mainly military so those characters will obviously know how to use their weapons; but different RPG's such as Fallout 3 don't make sense. Now, Fallout 3 is my favorite RPG and is easily one of the best, and is a great example of this cliché. The intro is about your character's child/adolescent stage of life, and at the 10 year mark, your dad gives you a BB gun and has some targets set up for you to practice on; now your character (I'm going to refer to them as he since it makes it easier) may have gone down there over the course of the next 9 years of the Vault 101 stage and practiced with said BB gun, but that doesn't mean he'll know EXACTLY how other weapons, particularly the energy weapons, work as soon as he picks them up. I don't think living in an enclosed environment for the first main part of your life will have you experience such things as PLASMA RIFLES! I think New Vegas did this better because your character is a 30-something year old courier. By that amount of time out in the wasteland you'd have actual experience with a lot of the different weaponry you come across, especially as a courier having to defend yourself.
I think, personally, that in an RPG such as Fallout, the amount of time you use with a certain weapon should increase your skill with it, like at the beginning of the game put some additional points in weapons/items you want your character to be skilled with, then as you pick up say, a plasma rifle, it'll be a lot less accurate, more kick, longer time to reload; all that because your character doesn't know how to work that particular item, and the more you use it the better you get with it. Skyrim did this, but to a lesser extent, only having the experience gained add more power and abilities you can do with that skillset;
but Far Cry 3 did this amazingly by having Jason not too familiar with guns as a soldier would be, but then as the game progressed, got more skilled with them.
I don't know, this cliché isn't overdone too much, but when its there it takes me out of the experience and has me question
how the protagonist knows how the item works.
Captcha: take wrong turns. Well that's not good life advice, captcha