Daniel Green, 26, claims he has a ten inch member with a four inch girth and has often had problems having sex in the past.
He allegedly attacked the 29-year-old after a night out in the City.
Green and his colleagues brought the alleged victim and her friend back to their StratX headquarters on the fourth floor of an office block near Monument for a wild bash.
But she crawled under a desk for a sleep until she was able to catch the first train home because she did not have enough money for a cab, the Old Bailey heard.
Green said he had ended up in the empty office because he had been looking for a place to charge his phone.
The stockbroker said he and the alleged victim complained about a friend who had ‘ruined the evening’ by claiming her cocaine had been stolen when in reality she just did not want to share.
He said they had consensual sex but she started crying because his 10″ penis – which he claims is 4″ in circumference – was just too large.
“She was touching me, she unbuttoned my shirt and she was touching me, also we were still kissing,” he said.
He claimed they had taken off all their clothes and were lying under a desk in the ‘spoons’ position when he tried to enter her.
“I’m kissing her neck, she’s putting her arm around me and at which point I tried to penetrate her with my penis.
“A which stage she rolled back, and at that point I saw a tear in on her face so I jumped back and I said ‘Oh f*** are you crying?’.
“I thought my penis was hurting her. I always have difficulty when it comes to having sex with girls, I find my penis is hard to penetrate females unless there is lube readily available.
“The last relationship I had we didn’t have sex a lot, if we did manage to do it would cause her pain and we wouldn’t be able to have sex for a few weeks.”
When asked how large his penis was he said it was 10″ long and 4″ in circumference.
Green made a ring with his fingers as he estimated his girth to the jury.
“I tried to penetrate her twice,” he said.
“She said: ‘Can you leave? Just leave, just go’.”
He said he grabbed his clothes and fled the office and that the whole incident had taken less than two or three minutes.
Green said that earlier in the evening while in a club he had asked the complainant if she was okay, saying ‘that’s just the kind of guy I am’.
In her evidence, the victim said: “I absolutely didn’t consent to sex with Daniel, it was rape and I was trying to get away.
“I didn’t shout out for someone to come and help me, my focus was in trying to get away.”
She estimated the whole incident lasted about a minute-and-a-half, and said Green had been making sexual noises during that time.
Prosecutor Timothy Forster told how the alleged victim and her friend were out in the City on Friday 15 May last year.
They met up with Green, who had been working for StratX for only a week, and his colleagues at a bar in the City.
The group had all been drinking and taking cocaine.
The alleged victim said she had drunk three glasses of red wine, taken three pinches of cocaine and one line of cocaine while out in the City.
In the early hours of Saturday morning one of the revellers suggested they should continue the party back at the StratX office, in Abchurch Lane, where the group continued drinking, taking cocaine and listening to music.
Jurors heard the complainant did not have her bank card or enough money for a cab and had decided to rest until she could catch the first train home. Laying in the foetal position under a desk when she felt Green grabbing at her legs before ripping off her trousers and knickers.
After the alleged attack, the complainant phoned a friend, who in turn called police.
But when officers arrived, Green had gone and was later tracked down at his home nearby.
Jurors heard he gave a prepared statement denying the alleged rape and made a similar statement in November last year.
Green, of Walthamstow, east London, denies a single charge of rape on May 16 last year.
The trial continues.