A strikeout means you failed just like the baseball term. As with a lot of baseball terminology, this applies well to dating and relationships. Applied to dating, this means you did not score a date or get lucky like on a white night stand.
There are two ways to strikeout as in baseball. To strike out swinging, that means you tried every hard but you still failed. Most likely because you tried too hard and the girl thinks you're wasting her time or you're just not good enough. You keep swinging, but you keep missing. But at least you tried.
The other way to strikeout is to strike out looking. That means the opportunity was there but you fucking wasted it but not doing a goddamn thing. The girl is sending you signals at the bar but you just ignored her. Maybe because you were worried about cheating on your girlfriend. Who knows what happened next? Your best friend scored with her. The guy next to you scored. The bartender scored. The bouncer scored. Or even the underage frat kid you insulted earlier scored. But you didn't. Why? Because you never tried.
Brad: "How was the bar last night?"
Jeremy: "Great man. There were some really hot chicks there."
Brad: "Did you score?"
Jeremy: "I fucking struck out on all of them."
Brad: "WTF? Strikeouts on all of them?"
Jeremy: "Yeah I struck out swinging. I guess because some skank threw up on me."
A: "Dude, wtf bro. You just struck out looking."
B: "What?"
A: "She was sending you signals man. She was into you and you completely ignored her."
The act of taking a of marijuana out of a bong, then take a shot, chug a beer, and then eat a banana. all in one breath.
"It took me 3 trys to finally master the Tropical Strikeout! I was so high after that."