This is a guess, but it could be a colloquial version of ペコペコ熊, which would basically mean 'hungry bear'. To me, saying /paykokumah/ is a bit difficult, and it almost sounds natural to shorten it into /pay'kumah/. So, the translation:
ぺっクマのあの引きつった顔ったらなかったぜ!わははーーっ!!
ぺっ熊の = angry bear's
引きつった顔 =...