Give the kid a chance to learn. Everybody was ignorant once, and it's not impossible for a bright person to have had lousy information pooped into his/her head from a friend or other source that seemed to be reputable - before knowing better.
However, if the kid still doesn't learn after the second or third time around (and still talks about squeezing 400 horses out of his 318 as if it's something entirely doable on a budget), THEN he's damn brick stupid beyond a shadow of a doubt.