Need a Japanese translation of a shirt?

Question

I got this shirt on a street market in Osaka whilst on vacation. Please someone help me translate what it means! The guy who sold it tried to explain it was a joke, like a play on words, but I need more than that.

Front of shirt:
http://img91.imageshack.us/img91/851/pict0004cz8.jpg

Back of shirt:
http://img85.imageshack.us/img85/3584/pict0003ff1.jpg

Answer 1

On the front the big letters, '落花生' mean peanuts in Japanese, 'Rakkasei'

On the back, in Large letters it says

ぴい夏
pi- natsu、which when read in Japanese sounds like 'peanuts'

I'm not sure what the pi- is supposed to mean, but 'natsu' means Summer in English. It is kind of like a pun.