Loser
noun
You've hopefully come across 負ける by now, which means "to lose." So, you can figure out this word means "losing dog." Well, calling someone a dog isn't so nice, so you're probably just calling them a loser.
まけいぬ
The readings are kun'yomi, but you should be familiar with 負ける and of course 犬 well enough to learn the reading here.
私はあなたのことを負け犬だとは思わないよ。
I don't think you're a loser.
こんな生活をしてたら、ずっと人生の負け犬だよ。
If I am living like this, I'll just continue to be a loser in life.
負け犬と呼ばれるのは、もう嫌なんだよ。
I don't want to be called a loser anymore.