Bad
Poor, Wrong
い adjective
This is a single kanji with an い on the end, meaning you know it's probably an adjective. What's the adjective form of bad? It's also bad.
わるい
Since this word consists of a kanji with hiragana attached, you can bet that it will use the kun'yomi reading. You didn't learn that reading with this kanji, so here's a mnemonic to help you:
Do you know how in the Mario universe all the bad versions are called "WARU" (わる)? For example: "WARUIJI" and "WARIO." That's because they are bad. They come from this kanji. So, if you ever need to remember this reading, just think back to Wario and Waruigi.
この食べ放だいのすし屋のせっ客は、しんじられないほど悪い。
This all-you-can-eat sushi restaurant's customer service is unbelievably bad.
悪いけど、この野さいちょっと蒸しといてくれない？
Sorry to bother you, but can you steam these veggies for me?
牛乳は悪くなっていたけど、俺は気にしなかった。
The milk went bad, but I didn’t care.