There are many Ego cap awards, which are given to you for interacting with the environment and defeating bosses. These are the actions in each mission that boost Duke's health level. There is a tracker in the chapter select screen to check how many in each chapter you have.
Boss battles also increase the total Ego so the achievement will unlock after killing the Energy Leech if you follow the guide. Provided is a guide/checklist of "Ego Cap" locations to go along with the video. Items listed by appearance.
To save "Ego Cap" - you must reach a new Zone (Lady Killer -> Lady Killer: Part 2). Not just a save checkpoint!
Duke Lives 
Mirrors - Admire.
Toilet - , Pee.
Play Pool - (Pot all balls on the table)
Damn! It´s late 
Microwave Popcorn - Pick-up popcorn and place in microwave.
Autograph - or to Sign. (Counts but was not included in the guide)
The Duke Cave 
Dumbbell - to Pick-up, to Curl.
Bench Press - to Pick-up 100Lb weights, to Place on workout bench, to Use and Tap to complete a rep.
Punching Bag - to Punch.
Speed Bag - to Punch.
Basketball - to Pick-up, to Throw into hoop.
Pinball Machine - Beat the high score.
The Lady Killer 
Slot Machine - , Play any Slot Machine until you win.
Vegas in Ruins 
Defeat the Battlelord Boss.
The Duke Dome 
Photocopier - to Photocopy your behind.
The Hive 
Alien Wall Breasts - to Slap.
Queen B*tch 
Kill the Alien Queen Boss.
Duke Nukem's T*tty City 
Glory Hole - (Men's Toilet).
Tip the Stripper - (End of runway/catwalk).
Porno Tape - to Pick-up, to Place in DVD player (Main Office).
Poker Machine - , Win one hand of Poker (Game Room).
Alien Abortion - to Hit, Win one game of Alien Abortion, 850+ Score (Game Room).
Air Hockey - , Win one game of Air Hockey (Game Room).
Crash Course 
Frisbee - , Three can be found beside a Sports Bag on an outside ledge.
The Duke Burger 
Cigar - , At level start - Turn 180 and climb over the tentacle, run round the corner and go through the Red Service door, found on the Shelf.
Porno Magazine #1 - , Found in the First Toilets before shrinking yourself.
The Mighty Foot 
Binoculars - , Found overlooking the Canyon (Left 1st Fuel Stop).
Computer Porn - on Keyboard, found in Security Office (With "Gas").
Ghost Town 
Porno Magazine #2 - Found in Church under broken seat (during driving segment before town).
Dam Top 
Kill the Battlelord Boss.
Paper Airplane - , , Found in back of School Bus on the Dam Top.
The Shrunk Machine 
Calendar - After collecting the Freeze Gun, enter the room and reach the Back Office.
The Forkstop 
Porno Magazine #3 - Found at the Start of the Level, behind the first opened door.
Generator Room 
Kill OctoKing Boss.
All unique "Ego Caps" done previously.
All unique "Ego Caps" done previously.
Blowin' the Dam 
Kill the Energy Leech Boss.
The video shows the earliest points to earn the Ego.
I know there's a photocopier and paper planes which are sort of not obvious, and then there's all the porn mag's lololololol everything else is quite straight forward but I still don't have this either.
Weird trick for you guys. I know how frustrating the pool table challenge can be;I got so frustrated I decided to try something ridiculous and it worked. In the game room at Duke's Titty City (no way of doing this with the pool table in Duke Lives!); go grab one of the basketballs from the throwing game. Throw the ball at the pool balls. It's still hard to get them to go in and you have to keep looking for the basketball after it gets on the ground, but your odds of scratching or having a ball fly off drop significantly; the latter becoming impossible.
Wow that seems like an amazing trick there Bcadren, I would probalby do that if I didn't already have the pooltable thing completed...for me it was more being patient and hitting the white ball before it goes in a hole.
Hey, just for a heads up there is a tricky ego cap that I don't think is necesarily mentioned in the guide. If you go to The Lady Killer mission and try the benching ego cap with all 6 weights on you'll get another ego cap aside from "just doing a rep". Btw the other weights can be found in the room to the right while engaging Duke Vision.