The defendant appeals his conviction, after a jury trial, of assault in the second degree, attempted grand larceny in the third degree and two counts of attempted robbery in the second degree. The District Attorney concedes and we agree that the attempted grand larceny would be dismissible as an inclusory concurrent count, under CPL 300.40, of the attempted robbery (People v Rivera, 46 AD2d 642).
Although there were other witnesses to the defendant’s flight from the crime area—a flight that the defendant testified was caused by panic when he realized that the victim thought that he was in league with one who had attempted the robbery and raised a hue and cry against him—there were only two witnesses to the crime itself, the victim who inculpated the defendant and the defendant who portrayed himself to have been an innocent bystander. To reach a verdict of *434guilt, the jury had to grant credibility to the victim and deny it to the defendant. Several errors attended the trial and, since we cannot say that they did not affect the resolution of this basic credibility question, we cannot hold them harmless (People v Duncan, 13 NY2d 37, 42).
A jackknife had been found in the defendant’s pocket when he was arrested. No account by the victim at the trial nor any other time mentioned a knife, nor did any count of the indictment. The prosecutor brashly displayed it before the jury, announced that it was "a dagger” with the words "Big Bruiser” on it, and then elicited testimony that it had been found on the defendant. This irrelevance can have had no other purpose than to prejudice the jury against the defendant. (See People v Freytes, 48 AD2d 807.)
The defendant admitted that, although he was now free of drugs, he had used them formerly including the time that he had worked for the Burns Security Agency, but that he had not been asked about drugs when he had applied for that job. Through the device of couching it in repeated questioning, the prosecutor himself testified that the Burns application form contained a question about drug usage and concluded for the jury that the defendant must have lied when he answered it. Such prosecutorial testimony, without more, has been held reversible error in a case similarly involving a credibility question between the defendant and a victim (People v Duncan, supra; see, also, People v Petrucelli, 44 AD2d 58).
The prosecutor cross-examined the defendant repetitiously and at length. Many of these questions, the first time asked, properly related to the issue of the defendant’s credibility (see People v Duffy, 36 NY2d 258). The repetition of them, plus the prosecutor’s excursions far afield—had the defendant cut classes in high school, were his friends ever in the high school auditorium after it had been closed for the night, were his parents aware that he had been cutting classes, did he steal the lunch money of little children—all convince us of a design to improperly convey criminal propensity to the jury (People v McKinney, 24 NY2d 180; People v Buzzi, 238 NY 390).
The jury may have been misled as to how to assess the defendant’s credibility. The court charged, "The mere fact that the defendant is an interested witness, that in and of itself effects [sic] the credibility and the believability of his testimony”. That could be interpreted to call for a discount of credibility because of interest. Such would be erroneous (see *435People v Ochs, 3 NY2d 54, 56) and especially harmful where credibility is the only issue.
Despite the defendant’s failure to preserve by objection or exception all of those errors for review, the interests of justice and the exercise of discretion require a reversal and that the case be remanded for a new trial.