ダサい is negative slang for clothing or style that seems unfashionable or lame. Speakers use it as a blunt criticism, and writers tend to put the ダサ portion in katakana.
Related expressions include:
恰好よくない (not good-looking; not stylish)
恰好悪い (bad-looking)
おしゃれじゃない (not stylish; not smartly dressed)
Depending on context, English equivalents include “unfashionable”, “uncool”, “lame”, and “dorky”.
Nishikata and Takagi meet up at the library to study. Although it’s hot out, and Nishikata ran to make it to the library on time, he refuses to remove his sweater.
西片:
「今日のＴシャツは… 母さんが買ってきたなんかダサイやつ！！」
“Today's T-shirt is...some dorky thing my mom bought me!!”
Housenka from the monkey squad appears before the dog squad, challenging them to a battle for their squad name. Before she can cause any trouble, Tsuwabuki and Mokuren from her squad appear to stop her. Housenka claims this is their chance to become the dog squad.
