In the teaser trailer, Oliver's shooting in the woods when Barry does an Arrow Catch, to which Oliver snarks "Show off." Not 30 seconds later, the ad shows Oliver priming three arrows, and Barry smirking.
Unintentionally, it becomes even funnier as the audience just sat through such an introduction seconds earlier.
Barry leaving his civvies behind in his rush to a crime scene, to which Harrison wonders how long it'll take him to notice. He has to buy a new outfit before heading in.
Just as the STAR Labs team figure out why Barry is suffering dizzy spells and fainting after using his super speed, Barry passes out... whilst running on a treadmill at super speed. Cue this blur of arms and legs suddenly stopping as Barry flops to the ground, then gets launched backwards into a pile of boxes filled with packing peanuts.
Barry learns that Danton's cells replicate in a way only found in babies.
Iris: So what, your killer's a newborn?
Barry analyzes the scene of a robbery at a gun store, noting the perpetrator wears a size 10. Which he points out is just like the Captain. Cue him babbling to try and cover up what could have been perceived as trying to accuse the captain of armed robbery (Which he didn't mean)
Harrison Wells sarcastically applauding what he believes to be a two-faced Simon Stagg who had just said that he hopes Danton Black comes looking for trouble.
Iris asks Barry what he could see in her phone's photo of the red blur. Eddie calls at that moment.
Cisco messing up codes.
Cisco: We've got a two-thirty-seven in progress. Barry: ...public indecency? Cisco: Oops, I meant two-thirty-nine. Barry:Dog leash violation!? Caitlin: Bad man, with a gun, in a getaway car, go get 'im!
Eddie goes to the Wests' to meet Iris, but unfortunately runs into Joe, and had to quickly come up with an excuse that he wants to re-investigate the crime scene.
Barry asks which one is the north wing in the mall.
Wells: It's the one with the Big Belly Burger. [Cisco gives him a weird look] Wells: I eat.
Iris and Eddie finally tell Joe they're dating... and he reveals he already knows. This conversation results:
Eddie: So you're not mad? Joe: Oh I'm mad. If they hadn't confiscated my gun we'd be having an entirely different conversation right now. Eddie: ...I'll give you two some space. I'll be outside, looking into the Witness Protection Program.
He then gives his blessing on the relationship by promising Iris he'll do his best not to shoot Eddie.
Felicity is at a bit of a loss at an excuse for Barry's suddenly leaving—being used to saying Oliver is "on a date", or some other appropriate fib—and comes up with Barry having bad diarrhea. And then she berates herself for continuing to talk to the air after he runs off.
Her failing to dramatically crack her knuckles.
Joe and Eddie having a bit of an awkward time in the car while discussing Iris. Eddie turns on the radio...and gets "When a Man Loves a Woman". He switches stations...and gets "Let's Get It On". He promptly turns it back off.
Eddie: ...quiet is good.
A blink and you'll miss it one: Wells proudly says that Barry (running a few hundred miles per hour) isn't even close to his top speed...before hastily tacking on a "Theoretically, that is." Yes, he forgot to hide his knowledge of the future for a second there.
Barry and Leonard Snart bantering in full-costume makes for a fun moment.
The Flash: If you wanted to get away you should've taken something faster than a train. Captain Cold: That's if I wanted to get away.
Cisco threatens Snart with the prototype cold gun, which is so huge that Felicity and Caitlin have to carry around the power source behind him. After Snart leaves, Cisco mentions it's actually the lab's vacuum cleaner with a bunch of LEDs stuck on it.
Snart smiling at the "Captain Cold" moniker.
Iris telling Barry that Felicity likes him, since (in her own words) she's the only girl who sees him for the great guy she's always telling him that he is. Think about that for a second.
Episode 5: Plastique
When Barry realizes he can't get drunk (while they're having a pleasant night out at a bar), Caitlin squees about doing experiments and starts scrounging through her purse.
Barry: ...you keep a blood test kit in your purse? Caitlin: Hey, you have your hobbies.
Then in a Brick Joke at the end of the episode, Caitlin reveals that she's cooked up a very potent alcholic beverage (She calls it roughly 500 proof, 200 proof is pure alcohol) for Barry. When Barry says that he's gotten buzzed from it, Caitlin gets all giddy - and then it wears off after 30 seconds.
Joe: So, human bomb? Must be Tuesday in Central City.
When Eddie gets an emergency call interrupting the night out at the beginning of the episode, everyone else instantly pulls out their own excuses as to why they need to leave as well.
Barry tells Joe the Streak met with Iris, and Joe warns that Iris would have easily been able to recognize his voice. Barry demonstrates his ability to vibrate his vocal cords to produce a reverb effect—and Joe bursts out laughing.
Plastique blows up the suit in her first encounter with the Flash. Cisco begins sulking like a child & declaring her to be pure evil because of this, until he sees her.
Whilst the team are explaining meta-humans to Bette/Plastique, Cisco comments that none of them have looked like her. He immediately begins back peddaling, whilst a snickering Barry face palms & Caitlin threatens him with a lobotomy.
Whilst testing Plastique's abilities by giving her objects to throw & explode, Caitlin holds up a boomerang & gives Cisco a blank stare.
Caitlin: Didn't think this through, did you?
Episode 6: The Flash Is Born
When Barry recognizes the new metahuman as a childhood bully, Caitlin and Cisco starts reminiscing about theirs as well.
Caitlin: I had a childhood nemesis, Lexi LaRoche. She used to put gum in my hair. [pouts] Cisco: Jake Pocket. If I didn't let him copy my homework he'd give me a swirly. Barry: Now that we've established that we're all uber-nerds, what are we going to do about Tony?
Caitlin interrogating Barry whether he is secretly meeting Iris in costume while preparing to set his dislocated shoulder.
Barry: ...No. Caitlin: Good. [snaps his shoulder back in place with a loud crack] Barry: ARGH!
Cisco calculating the speed and the angle with which Barry has to hit the Girder (animated on a screen) while Caitlin looks worried.
Cisco seriously wanting to also hunt down his and Caitlin's childhood bullies, regardless of whether they also have powers.
Cisco and Caitlin are exchanging some technobabble when Wells wheels in and asks what they're doing. Cisco answers with that the're calculating the average amount of bugs Barry swallows when he runs. Wells comments he'll look forward to him receiving his Nobel Prize.
This exchange after Barry and Iris land blows on Girder, successfully knocking him out:
The Flash: Nice cross. Iris: I think I broke my hand. The Flash: [weakly] Me too.