If you are 0/7, don't flash and take the kill from your teammates who will secure it...
If you are 0/7, you are practically worthless in terms of gold. Now that you've net a kill, you're worth gold again. Not only do you hurt the team but you will for sure feed that gold right back to the enemy team. Just don't do it. It hurts the team and helps the enemy team.
EDIT to clarify I was 1 AA away from the kill with both flash and Wukong E up. The guy (MF supp) flashes over and gets the kill. He's nonstop feeding to Ezreal every minute. He could use the flash to maybe prevent Ez from netting a kill. Instead he selfishly wastes summ, takes kill from already snowballing Wukong (I was 4/1 she is 0/7).
get a kill in that exact scenario and make damn good use of it.