guard on

When someone in a recreational sport guards only one person through the entire game, usually because of a crush or something of the sort.

"Bro, in gym today Sally would not stop covering you. Thats a guard on if I've ever seen one."

"Hey, Mike... I'm kind of worried about you. At the Y earlier today, you definitely had a guard on for Jim. Does your wife know about this?"

card-on

1. When a person who plays trading card games (e.g. Yu-Gi-Oh, Magic the Gathering) enters a state of euphoria after acquiring a rare, valuable, or otherwise useful card, usually from a booster pack.

2. When a person who trades or collects cards of any sort strongly desires to obtain a specific card.

1. "Dude, when I pulled that Jester's Hat back in '92, I got such a card-on!"

2. As the young boy stared hungrily through the card store's glass front, he experienced his first card-on for the vintage Babe Ruth rookie card.