The regretful feeling of putting too many photos/an embarrassing photo on Instagram the morning after a big night.
"I instagret that photo I put up of me naked rolling around in my grandfathers ashes."
"Her box gap is smaller than it used to be, she'll be instagretting that photo this morning!"
A combination of the words "instant" and "regret;" the instant regret you feel after doing something incredible stupid and rash.
Lindsay was filled with instagret after telling her boyfriend that she still sleeps with a nightlight.