Ms Knox met Mr Seliber at the University of Washington
Amanda Knox said she was getting on with her housemates and having the "time of her life" in Italy, a close friend has told an Italian court.
Andrew Seliber, 22, a former roommate of Ms Knox, said she cared about her body and did not drink excessively.
But Mr Seliber said that neither he nor his friends referred to Ms Knox by the nickname, "Foxy Knoxy".
Ms Knox denies she murdered her British housemate Meredith Kercher, as does her then boyfriend Raffaele Sollecito.
Giving a character reference to the murder trial, Mr Seliber, from Boston, Massachusetts, said he met Ms Knox at the University of Washington where they shared a dormitory.
Describing an incident where she got into trouble with the police, he said: "We were all making too much noise and a lot of us helped her pay the fine."
Adding that she was a "close friend", Mr Seliber said: "She didn't drink any more than any other college student.
"We did a lot of rock climbing together, played music together, walked around the city together, talked and spent time together."
The pair maintained contact and Ms Knox told him about her life in Italy.
Mr Seliber said: "She told me she got on really well with her roommates and enjoyed the time she spent with them.
"She said she was having the best time of her life in a new country, enjoying a new culture."
Asked about her Foxy Knoxy nickname, he said: "It was not a name she called herself. I never called her Foxy Knoxy. I have never heard any of my friends call her Foxy Knoxy."