open goal

When there is a opportunity for a (painfully) evident joke to be made about something.

"...And she said it was really small!"
Someone who just stepped into the conversation:
"Your dick? LOL"
"Come on, dude. I know it was an open goal as soon as I would say that, but was that really necessary...?"

Open Goal

Easily accessible vagina

You'll definitely be able to get with her mate, shes an open goal