Someone who is attracted to the opposite
sex, but occasionally can be attracted to the same
sex.
A heteroflexible person can enjoy watching boy on
boy porn, but wouldn't do it in real life, could occasionally fantasize about males while masturbating, etc.
A heteroflexible couldn't imagine a future with the same
sex, and it's not on the same level as the opposite
sex they are attracted to. They constantly have identity crisis, sometimes they feel homoflexible, during high sexual drive, which is the opposite of what heteroflexible is, sometimes they just live their life as
normal.
It has more connection to pansexual than it has connection to bisexual, if anything it's a modern word for
bi-curious.
That being said a heteroflexible could lay down with the same
sex, but it would be nothing more than "just having
sex". It's situational, and they don't actively search for it, they could feel attracted just because they had a "good talk".