Basic Trope: Bob and Alice get caught in what looks like a sexual/romantic moment, but isn't.
Straight: Alice trips and falls down on top of Bob, leaving them in a position where it looks like they're in the middle of making out, right as Carol walks into the room and notices them.
Exaggerated: As above, except their clothes have somehow disappeared, they're in bed together, and their hands are in inappropriate places, yet there's still a perfectly innocent explanation for it all.
Downplayed: In a conversation with Bob, Alice makes an Accidental Innuendo, causing Carol to suspect that they're in a sexual relationship.
Alice and Bob have been practicing their reflexes lately. Bob actually turned around before Alice tripped, but the reaction of Alice made it so they ended up flat on the floor, not knowing Bob had gotten so good and thinking he would still be turned around.
Bob and Alice are having sex in a way that looks completely innocent when Carol walks in on them.
Bob and Alice admit that it is exactly what it looks like.
Alternatively: "This isn't what it looks like" and it isn't, and Carol proceeds to lay out, with ludicrous precision, the exact chain of unlikely events that led to their current compromising position.
Double Subverted: ...except that they were lying.
Parodied: Bob and Alice end up in a position like this practically every time they pass each other on the street.
Zig Zagged: Not even Alice and Bob are sure if this is what it looks like, or not.
Averted: The witness immediately assumes that there is a perfectly innocent explanation, no matter how bad the circumstances look.
Enforced: Alice and Bob are a particularly popular fan pairing, so the author puts them into a compromising scene as Fanservice.
Lampshaded: "I know this is like a line from a movie, but this really isn't what it looks like..."
Invoked: Bob immediately yelps the trope name when someone walks in on the awkward moment.
Defied: "Yeah, it's exactly what it looks like."
Discussed: "Let me guess ... this isn't what it looks like?"
Conversed: "So Alice and Bob got caught in a compromising position? I'm sure there's a perfectly innocent explanation for it."
Deconstructed: Despite her attempts to deny that anything happened, Carol spreads the word, and soon everyone at Alice's workplace "knows" about her sleeping with Bob. Alice is labelled as a slut by her peers, and the rumors put a massive strain on her platonic friendship with Bob.
Reconstructed: However, Alice's real friends refuse to buy into the rumors, and much prefer to get her side of the story instead.
Played For Laughs: Bob and Alice getting "caught in the act" is the result of a zany Rube Goldberg-esque series of accidents
Played For Drama: Bob's girlfriend breaks up with him after catching him with Alice in a Not What It Looks Like moment.