As Miya-san explained, やばい has so many ways to use. I'm gonna write some example sentences. 1.　あの人はやばいから、無視（むし）して。 trouble/weird/strange 2.　あの人やばい！ちょーかっこいい！　looks good. looks cool. looks attractive. 3.　やばい！しゅくだいわすれた。OMG! 　Oh,no! 4.　なにこれ、やばい！すごく、おいしい！Wow！awesome! Cool! So good! yummy! 5.　このゲームやばい。the best, I love it, addicting one. So, You can use the phrase almost anytime when you excited for good or bad, or when you feel a trouble is coming. 今日の私の”やばい”こと、それはバレンタインデーのチョコを食べすぎてしまったこと。ぜったいふとった。やばーい！！

It sometimes means "cool", sometimes "dangerous". あの人やばい！かっこいい！ means "cool" あの人やばい！こわい！ means "dangerous" We also use やばい in both negative and positive way. like when something is beyond expectation or surprisingly good or bad. There's too many way and no specific way to use. この新しいゲームやばいよ。 This new game is super. 彼はやばい人だ。 He is insane. やばい には大きく二つ意味があります。 昔から使われている 例) どうしよう、課題の提出が間に合わない！やばい！ という、困ったときや焦ったときに使うterribleのような意味の 表現と 若い世代でよく使われている 例) この人かっこいい！やばい！ などは、 凄い！とか最高！というawesome に似た褒め言葉としても使います。

I am 50s. I use yabai only for dangerous. I was surprised to hear yabai was said by a university student in front of nice food. All middle aged adults sitting nearby were disappointed to hear it. Because, we think well educated Japanese dont use yabai for nice. Yabai itself is not elegant word. So, I use it to warn someone that I think that information is dangerous. Sono hanashi wa yabakunaidesuka ? Sono hanashi wa chotto yabai to omoimasuyo. yabai hanashi means someone is trying to cheat you, or related with Mafia.

I'm in my twenties so let me answer you question from a young person's point of view. I use やばい for EVERYTHING,(only when i'm with my friends) so the meaning of やばい depends on context like Miya and Yoko say. Eg: この靴やばい　（=These shoes are so nice / ugly)