[Now, this is a Creative Writing assignment. Please understand that I SUCK at prose, and that I made it through the first half of the class writing mediocre poetry that my teacher liked. Now I actually have to work. This is a thing that needs help. The assignment: Write mostly dialogue. Help it! Help it!]
He drew roses on the table with his fingers and looked out the window. Which one would she be? he wondered. The one in the silver sedan? The girl with too many rings on her right hand? The one pushing a stroller? He knew only that he knew nothing.
“Mark?”
He twisted around. He hadn’t even seen her come in, and there she was behind him. “Laura?”
“Yeah! It’s…amazing to meet you,” she said, extending her hand.
He reached out slowly. He let her thumb and four short fingers scrape across his palm before finally grasping hers and sputtering out the inevitably redundant greeting. “Nice to meet you, finally.”
She sat down opposite him. His jeans rustled slightly as he drew his legs back. He’d spilled coffee on his shirt.
“So…why’d you pick this place?” he said.
She laughed and motioned to the folded waitress’s uniform in her bag. “I work here.” So that’s why he hadn’t seen her come in.
“I’ve never been here before. Well…I guess that makes sense. I live an hour away.”
“Oh, I’m sorry! I didn’t know you lived that far! We could’ve met down the road a ways if I’d known,” she said.
“No, it’s okay. You work here? I thought you were in college.”
“Oh, I am. Yeah, this place is far from campus, but I hate running into other students, so here I am.”
“I hated that too. One time I even had to serve my English professor at the restaurant I worked at, and he got drunk.”
She giggled nervously. “Well, thank God that hasn’t happened to me.”
“So, Laura, I…I just realize that I…know nothing about you. I should, shouldn’t I? I mean, we only met a little while ago on the freaking internet, and it’s kind of a shock to find out your father had another child and you have a...sister...out there, but really...”
“Well, it’s not like I know any more about you, huh?”
His relief at her nonchalance was evident. She noticed that his grin was crooked. “Well,” he started, “I…work at a bank. Kind of boring.”
“Really? Well, you know I’m in college. I’m studying engineering.”
“Nice.” He grinned.
Her pager buzzed. “Oh, crap,” she muttered, “I have to go. It was wonderful to meet you…” Her voice trailed off.
“Yeah, I can’t believe all of this,” he said. “Sis,” he added, like a weight to the conversation.
“Well,” she answered, shaking off the awkwardness again, “I’ll see you, bro.” She kissed him on the cheek and clattered out the door.
“Kate?”
She turned, now safely out of Mark’s range of vision. “Everything went fine, Captain. He’s bugged.”
“Bro? Nice touch, Kate. Very believable.”
“All in a day’s work, Sir.”
You said a lot of he did, she did, his, her. That kind of thing, which after a while got a tad bit weird, you could have said their names more often, just to help with the flow.
As for the dialogue, (which was the assignment right?) it was good, very believable and flowed well too, the only suggestion I could make for that would be to add a little bit more description. 
Anyways, well done, I love the twist you added in at the end =D, very cool. Keep up the good work!!!!
