Cool Loser: Zigzagged. When he actually picks up (or at least is close at picking up) girls, it's usually because they fall for his peculiar humor or pertinent sarcasm. But most of the time, these traits just make people consider him to be a pompous/awkward freak.
Deadpan Snarker: Particularly in the narrations. In fact, it's what women find most attractive in him.
Digging Yourself Deeper: Has a tendency to keep going off on tirades long after he should have stopped, most notably in his rebuffing of Kerri.
Not so Above It All: While he generally attempts to behave more grounded and rationally minded than most of his friends and is clearly more responsible in the majority of situations, there are several incidents that prove he is effectively capable of the same level of thoughtlessness and ineptitude. Most evident when he's left home alone, he eventually joins in with the lads in destroying daffodils after a few cans.
The Smart Guy: Somewhat subverted in that he's while he's academically bright and smarter than the other three, he often reveals his limited amount of social skills and general impulsiveness in particular situations.
Socially-Awkward Hero: He could be interpreted as this as he has undertaken some misguided deeds that express his ultimate lack of understanding certain societal norms. Such as:
Vocally complaining when a group of people were seated at the front of a ride he and his friends had specifically queued for, only to find out said people were obliged to take this space in the ride as they were disabled.
Somewhat justified, in that he had no knowledge of their disability, having never previously seen these people, and he also showed extreme remorse for these actions.
Impulsively placing a wig within his underwear during a date with an older woman, after a prank lead to his own pubic hair being removed, causing further embarrassment for him.
Attempting to amiably break off an effectively one-sided relationship with a girl he was never attracted to, only to create a scene during his friend's birthday party.
This was partly the girl's fault; she had manipulatively claimed that Will attempted to have sex with her, prior to breaking off the "relationship".
Becoming the subject of abuse after making several pretentious, patronising but ultimately not malicious claims towards a group of garage workers he would be employed by during his work experience.
Claiming to have engaged in several sexual encounters in order to secure his relationship with a slightly older, promiscuous girl, only to face more severe humiliation when his lack of sexual experience is evidenced.
Making wild claims of said girl's opinion of him and an extreme exaggeration of their "relationship" to avoid being further abused by the afore mentioned group of mechanics.
Surrounded by Idiots: He is academically more knowledgeable than his three friends and usually more grounded uptight and sensible than them (other than possibly Simon, as the voice of relative sanity alternates between the two characters depending on the situation)while he has his own moments of tactlessness, he is generally among the most rationally minded and logical of characters in the series.
Hopeless Suitor: To ridiculous levels with Carli. He's pined for her since he was eight years old and doesn't get anywhere with her until the end of series 2, and even then, she doesn't really care about him.
It's All About Me: When his father tells him that the family will need to move to Swansea so he can keep his job, Simon goes mad, claiming that his life is ruined as a result.
Dirty Coward: Often; He immediately tells Donovan that Will is upstairs with Charlotte, mocks Simon after some guys threaten to beat him up over something Jay did, ditches his friends when some chav pre-teen girls get their brother to chase them with a baseball bat...
Drives Like Crazy: In contrast to Simon, who drives like an old woman, Jay is extremely reckless behind the wheel of his mother's car.
Freudian Excuse: The way his Dad treats him explains a lot of Jay's behaviour.
The Nicknamer: Almost never calls Will by name in the first two series, but instead some variation of "briefcase". In the third series, when Will becomes more known for shitting himself at an exam than carrying around a briefcase, Jay starts calling him by name, though still lets slip a briefcase insult/joke once in a while.
Sir Swears-a-Lot: Probably has the filthiest mouth out of the lads, although they have their moments too.
Token Evil Teammate: Evil is a strong word, but most of the time, Jay isn't actually nicer than school bully Donovan - the main difference simply is that Jay is too big of a coward to use violence. His jerkassery is played more for laughs than Donovan's, though, but except for his very few Pet the Dog moments, he only seems to be part of the group by virtue of having known Simon since early childhood and being admired by Neil who is stupid enough to believe in his lies.
There's also the fact the lads are clearly aware of Jay's Freudian Excuse- Simon even accuses Jay of be being scared of his Dad in the movie. Donovan on the other hand mostly seems to act like a dick For the Lulz.
What You Are in the Dark: When he talks alone with Big John in the sixth episode, he shows a surprisingly nice side of himself and even seems to find John sympathetic. However, when others are around, he doesn't miss one chance to gravely insult John, especially about his weight - because the general consensus is that John is a loser.
"Well Done, Son" Guy: A lot of his lies are to impress his Dad, but his Dad is Genre Savvy enough that he doesn't fall for it. Unfortunately, he then tends to respond to Jay's attention seeking by belittling him.
Played by Blake Harrison
Anything That Moves: He's not fussy about who he winds up with, which is probably why he's the first of the lads to lose his virginity.
Cloud Cuckoo Lander: Particularly when he goes on about how many things are drugs, starting with relatively sane things such as cigarettes and alcohol and moving on to stuff like trainers and clingfilm.
Nice Guy: Neil can be annoying due to his stupidity, but he has almost no actual Jerkass moments compared to the other lads. He is also generally polite and is quick to comfort his friends in the "arm around the shoulder and kind words" way that the others would probably deem as too "bent" or girly.
Jerk with a Heart of Jerk: Will thinks he's a good enough guy to help Neil out once (he thinks) he got a girl pregnant. He's wrong.
He does at least stop Mr. Kennedy from trying to molest Neil several times, so at least there's that.
Not So Different: Despite hating Will with passion most of the time, he genuinely agrees with him when Will argues that a fashion show is a stupid, unethical way to collect money for charity since only good-looking people are able to take part. However, he is still enough of an asshole to force Will to take care of the charity money anyways.
Pet the Dog: Neil mentions Gilbert takes him making a move on Ms. Timms after one too many beers quite well.
Sadist Teacher / Apathetic Teacher: The former against students who have managed to personally annoy or insult him, especially Will. The latter against students in general.
Straw Loser: He often appears when the four main characters seem to be complete losers to point out that they are actually not at the bottom of the hierarchy (there is a reason they're called "inbetweeners" - they're not really losers, at least not if they pull themselves together, but they are surely not popular either), because guys like John are much worse off.
However, it's inverted in the episode "Will's Birthday" where the fact that even John is invited to a party shows how uncool the four main characters are.
Although, when confronted, the girl in question says the only reason she didn't invite the lads simply because she didn't know them that well.
The Comically Serious: Or The Cringe Comically Serious if you want. Whenever he goes into unnecessary details about his sex life, he often has a completely deadpan face as if he thinks mentioning his sex life is just like discussing politics. This tends to embarrass Simon even more.
Reasonable Authority Figure: He waits to hear Simon's side of the story when Simon accidentally climbs into Carli's little brother's room and professes love to him.