Meaning:
shameless, impudent, brazen

Usage example:
面接に無断欠席した男がいけしゃーしゃーとまた応募してきたことに驚いた。(I was surprised that the guy who failed to show for his interview was brazen enough to apply again.)

Variations:
いけしゃあしゃあ, イケシャアシャア