ηζ γγΌγγγγ (n) (1) stupidity; idiocy; (2) blockhead; idiot; dimwit; mediocrity [G][GI][A] not "Bonklers" even if old fansubs did say that
For more recent comparison, think of Futami Ami & Mami in The Idolm@ster, who perform under the stage name Ami's. Randomly adding on English plurals to Japanese text isn't common, but it happens.
Blockheads
They formed a club called the "bonkuras" since they all got bad test scores.