In chapter 25 Shinji and Asuka have a serious, soul-baring talk. However she had just taken a shower and Shinji found her cleavage and her legs very distracting. He nearly got caught several times ogling her.
In chapter 47, holographic illusions featuring -among other things- beautiful human women are used to lure the enemy soldiers in a trap.
In chapter 48, Shinji is so distracted staring at Asuka's butt that he bumps against her. Later Misato uses her female charms to distract the warlord ruling the city.
Advice and Trust: In chapter 3 Asuka and Shinji are pretending to have a fight. However Asuka is wearing nothing but a towel and Shinji is so busy ogling to her bare legs that he is barely paying attention to what she is telling.
Last Child of Krypton: It happens to Shinji when he first meets Asuka. He stands so distracted, gawking at her, that he forgets where he is.
Nobody Dies: When Asuka first gets into her plugsuit as Unit-02's new pilot (it's a long story), Shinji walks by one the way to a test. Once he gets a good look, a wall decides to say hi. Combining this with the multiple situations of Did I Just Say That Out Loud?, it's a wonder that Asuka hasn't gotten over her socialization issues.
Earth and Sky: Happens repeatedly to Apple Bloom around Pipsqueak. Then they hook up, and it starts happening to him.
When Spike gets a good look at Quillina the dragoness in chapter 24, he ends up chewing on his pen and trying to write with a piece of agate he was snacking on.
In The Wizard in the Shadows, Harry is angsting about the oncoming army of Mordor and moans that not even Weasley Wizard Wheezes exploding could distract him. Ginny is wearing a Modesty Bedsheet and takes this is a challenge. Ginny drops said bedsheet.
Naruto:Asunder: Naruto's reaction to Hinata wearing a skintight body suit (He fought of the nosebleed). Not helped by Hinata thinking Evil Tastes Good and teasing Naruto the whole time.
Escape From The Hokage's Hat: While out shopping for new clothes and supplies (they've been out in the wild for 4 months) Hinata asks for Naruto's opinion on her new outfit. What he sees is her wearing a blue version of Tsunade's top with a spandex one piece that stops at mid-thigh at the bottom and shows off her Absolute Cleavage up top. He's quiet for a beat before blurting out how hot she looks.
Origin Story: Alex Harris is a magically created clone of Power Girl, so what else would you think happens? While Alex expects people, especially men, to react like this, and uses this to her advantage, she can still get annoyed by it.
Tony Stark acknowledges that he has a tendency towards this, and is ashamed to admit that it does interfere with his professionalism. He does try to not be distracted by Alex when he realizes he has been ogling a 17 year old girl.
In the Empath: The Luckiest Smurf story "My Unsmurfy Valentine", Vanity gets so distracted by Smurfette after he runs into her that it takes a while for him to snap back to looking at himself in his mirror.
At one point in Portal 2: The Unauthorized Musical, Cave asks Caroline how he looks for their trip to Black Mesa. Caroline gets lost in thought, realizes it, and awkwardly blurts out, "Science!... sir!"
Cave: You always know what to say.
In The Bridge Fancy Pants and a few other stallions gawk and stumble over their words when they meet Mothra Lea in the form of an Alicorn Princess.
In Ninja Wizard Book 5 Ron runs into a tree while trying to follow a pretty blonde in a slit skirt and bikini top.
In Scrap Value, Xander and a quartet of Skrull infiltrators watch an android of Black Widow practice her martial arts naked. Not a single one of them is capable of actually paying attention to the parts of her body she's attacking with, instead focusing on things like her chest when she does a spin kick.