Bob does a Sherlock Scan of two random strangers, picking up the subtle hints that they are in love, yet fails to notice Alice's far less subtle hints.
Zig Zagged: Alice ignores Bob's advances, but then blushes towards small flirts, which she forgets, and then he moves on. Alice becomes jealous and takes Bob back for herself, but then forgets why the next day. Essentially, Green-Eyed Epiphany meets "Groundhog Day" Loop.
Averted: Bob understands what Alice means the entire time.
Enforced: "Alright, how can we drag out the sexual tension between these two?"
"I don't get it, Maria. I keep trying to ask him out, but he keeps giving me these vague answers."
Bob: "How do you think I can find love?" Charlie: "Well, getting rid of your Alice-shaped blind spot would help."
Invoked: Bob is very aware of Alice's interest in him but doesn't want her as a girlfriend. So he hopes that by invoking this trope and feigning obliviousness she'll eventually stop trying to woo him.
Defied: Alice decides to sit Bob down and clearly enunciate her feelings for him.
Discussed: "I don't understand it. How can Bob be a whiz at picking up non-verbal cues from everyone around him but fail to notice I'm crushing on him? He can't be faking it... right?"
Conversed: "It's a wonder Bob is so clueless.", "Don't forget Alice, she could always just ask outright and see what happens."
Deconstructed: Alice gives up on Bob because he never gets the hint. He misses out on what might have been an incredibly fulfilling relationship.
Reconstructed: Alice eventually succeeds in letting Bob know how she feels.
Played For Laughs:
Alice tries to get Bob's attention to the point she kisses him, but Bob, as clueless as he is, wonders why Alice kissed him in the first place, causing a Mood Whiplash to her and the audience in the most hilarious way.
Alice go to absurd lengths to let Bob realize her feelings, including holding a giant neon sing and numerous Zany Schemes.
Played For Drama: Alice's inability to get through to Bob sends her into a deep depression.