Minty hot is derived from the two words "mint" as in "mint condition" and "Hot" as in "She/He is HOT!!"
When something looks like its in good shape and hasn't been used much and it is extremely eye catching at the same time, it is minty hot. It can be used for people as well as inanimate objects.
Hey man, last night I had sex with this woman from Gambia! Dude, she was Minty Hot! Hardly used and looked good!