Jim:
I used to have an imaginary friend called Lionel. Used to steal all my girlfriends. he was so cool.
Tom:
why did you not imagine him as a geek?
JIM:
what, have everyone think I hung out with nerds. it gave me street cred hangiong out with a cool bloke.
The wording needs a bit of polishing, but I like it. 
This reads as stand-up gag that's been adapted which only negates the joke.
Its a funny joke but needs to be part of something bigger like a stand up routine or longer sketch/sitcom(which is a bloody long sketch 
)
As others have suggested, this would be a good passing comment in a longer sketch or a scene from a sitcom, but not a whole sketch based around it. Keep it on file though....hang on, is this Jim fella the same "Jimmy Shoe", if he is then you could quite easily use it in your sitcom.
geek
"sideshow freak," 1916, U.S. carnival and circus slang, perhaps a variant of geck "a fool, dupe, simpleton" (1515), apparently from Low Ger. geck, from an imitative verb found in North Sea Gmc. and Scand. meaning "to croak, cackle," and also "to mock, cheat." The modern form and the popular use with ref. to circus sideshow "wild men" is from 1946, in William Lindsay Gresham's novel "Nightmare Alley" (made into a film in 1947 starring Tyrone Power).
computer geek jargon
(Or "turbo nerd", "turbo geek") One who eats (computer) bugs for a living. One who fulfils all the dreariest negative stereotypes about hackers: an asocial, malodourous, pasty-faced monomaniac with all the personality of a cheese grater. The term cannot be used by outsiders without implied insult to all hackers; compare black-on-black usage of "nigger". A computer geek may be either a fundamentally clueless individual or a proto-hacker in larval stage.
See also Alpha Geek, propeller head, clustergeeking, geek out, wannabee, terminal junkie, spod, weenie.
[The Jargon File]
(1997-06-26)geek Slang.
–noun 1. a peculiar or otherwise dislikable person, esp. one who is perceived to be overly intellectual.
2. a computer expert or enthusiast (a term of pride as self-reference, but often considered offensive when used by outsiders.)
3. a carnival performer who performs sensationally morbid or disgusting acts, as biting off the head of a live chicken.--------------------------------------------------------------------------------
[Origin: 1915- 20; prob. var. of geck (mainly Scots) fool < D or LG gek]
Do you REALLY want to use this loathsome word!
In any case a Geek and a nerd are not the same thing, so to use both words is confusing.
Very strong idea, in a poor setting, the malignant imaginary friend, and you use it well. Just improve the structure.
Quote: billwill @ February 28, 2008, 1:20 PMDo you REALLY want to use this loathsome word!
Wow! You really don't like 'geek', do you Bill?
Quote: billwill @ February 28, 2008, 1:20 PMIn any case a Geek and a nerd are not the same thing, so to use both words is confusing.
But does joe public (the audience) know this? They're as good as identical in my book, and I am one.
Quote: Aaron @ February 28, 2008, 2:12 PMWow! You really don't like 'geek', do you Bill?
But does joe public (the audience) know this? They're as good as identical in my book, and I am one.
Did you observe that the dictionaries agree that it is OK to be used 'within the group' but for an outsider to use the word is considered an insult. Tht's how I feel about it.
I don't mind the word NERD as it has no other connotations, but intensely dislike the word GEEK. It creates an image in my mind of someone sitting at a computer keyboard with blood all over his face biting off live chicken heads.
Andrew - it's a good idea. The Mighty Boosh, before they were massive, were in a short film with this as the central concept. I believe it's still on the BBC film network.
Quote: billwill @ February 28, 2008, 5:31 PMDid you observe that the dictionaries agree that it is OK to be used 'within the group' but for an outsider to use the word is considered an insult. Tht's how I feel about it.
I don't mind the word NERD as it has no other connotations, but intensely dislike the word GEEK. It creates an image in my mind of someone sitting at a computer keyboard with blood all over his face biting off live chicken heads.
Wow. Ok. Well, each to their own!
We are talking about an imaginary person creating an imaginary person who is cool to hang with but stole all the girls (Who are also imaginary)being asked by a third imaginary person why he did not imagine his imaginary friend as a geek, and from this someone had visions of a person biting off the heads of chickens while hunched over a computer keyboard with bloody hands, Now THATS imagination.