1. under 18, as in jailbait
2. having not gone through puberty yet
"I would have gave it to her...but she's underripe."
looks good on the outside, looks delish, you get inside and its green, filled with thick black pips and it sour!
(attention whore, self obsessed, annoying and dosnt know how to stfu)
that boy is an underripe watermelon