People meeting at a bar is always a great setting in a thriller. Which people do you think are characters in your thriller? The two guys on the right, or the guy and two girls on the left?
I'd go for the two guys on the right. What are they talking about? Murder? Espionage? Kidnapping? Bribery? Information on a suspect? Maybe they're setting up a double-cross. Who are they double-crossing? The hero? Another bad guy who's trying to muscle in on their territory?
Is one from the FBI? CIA? Military? Is one of them a snitch for the hero? Does one of them know something that will change the course of the story?
Remember, prompts are only a jumping off point, something to stir the pot of your imagination. Anything can happen!
If you've never written dialogue and are afraid you can't, I promise that I've never worked with anyone who can't write dialogue, only with people who think they can't.
It's amazing what you learn once you free the character to say anything she or he wants to say! Dialogue is not only great fun; it's also a great way to get out of yourself and into character!