Touhid Rahman pleaded guilty in the ACT Supreme Court over the alleged incident that saw the 36-year-old Phillip man enter La Cruzada cafe, with a 20-centimetre knife demanding cash.
The manager of the cafe allegedly went to the kitchen, before grabbing a large knife, leading to Mr Rahman leaving the cafe.
Later the same day, police stopped him walking near the cafe and arrested him over the attempted robbery, with officers allegedly finding a screwdriver in his pocket.
Police documents reportedly say that while Mr Rahman was taken to a police car, he yelled in the direction of the cafe and accused its employees of lacing his pizza with cocaine.
Mr Rahman will appear in court again next week.