>something like this instead?
Yes, there are a lot!
Of course, the impressions change with different tones.
It is a little difficult to explain just with letters but let me try.
When you say this with a flat tone, this would sound quite assertive, meaning you are truly scared.
Contrary, with a going up tone like こわい(よ)ー↑ (plus with a smile), you are sort of enjoying the situation (I think).
The similar expressions in enjoying situations would be; こわ or こわー
怖すぎ[こわすぎ] NOT 怖いすぎ[こわいすぎ]:
In general, an adjective + すぎ is liked by young generations in their casual conversations.
I would say 怖すぎ [too scary]. But 可愛すぎ [too cute] sounds too much to me.
Young generations also like ちょー（originally ちょう; 超）可愛い [so cute].
ちょー is very casual. ちょーこわ（い）（ー） also works: ちょー + adjective.
め(っ)ちゃ可愛い is the same.
め(っ)ちゃ is originally a Kansai dialect (I use this a lot because I am from Kansai) but I often hear everywhere in Japan.
There are other (slangy) ways such as;
こわいし、こわいって、こわいってかんじ[I kinda feel scary]、
In your situation on the train, I can't guess what they said but I can see that they were enjoying the situation, which must have frustrated you.