Straight: Alice, who was formerly the most popular girl at Troperville High School, doesn't want to admit that she's single, and so she takes Bob (her cousin) with her to her reunion, telling everyone he's her husband.
Exaggerated: The two of them wear a wedding band set to the reunion.
Downplayed: Alice gives a fake married name at the reception and gives an excuse for why her husband isn't with her.
Alice doesn't want either the other women losing respect for her because she's single, or the men that she didn't like then (and doesn't like now) hitting on her.
Alice is a lesbian, but still in the closet because of what others might think.
Inverted: Alice is Bob's real wife, but he treats her as though she were merely his friend or sister, for one reason or another.
Zig Zagged: Alice is always concerned about her image. So sometimes she travels around with an attractive male friend or relative, claiming that he's her husband to impress others, other times she does not, depending on the situation.
Alice goes to the reunion alone, and does not claim to have a husband or boyfriend.
Alice truly is taken and goes to the reunion with her real partner.
Enforced: The writer is trying to show Alice's insecurities as a Christmas Cake, a closeted lesbian, someone who's ashamed of her real husband, or whatever else the plot demands.
Lampshaded: "Did you say "husband" or "cousin"?"
Invoked: Alice goes to adopt a child, but is told that the only thing preventing her from being allowed to adopt a child is her lack of a husband.
Defied: Alice knows that lying only causes more trouble, so she's honest about her single status, her sexuality, etc.
Discussed: "How'd Alice get a boyfriend on such short notice?"
Conversed: "How exactly do you explain to someone that you need them to fake being your husband?"
Deconstructed: Someone is bound to be hurt or embarrassed (or both) by all this deception...
Reconstructed: Alice confesses the truth, and learns that no one would have lost respect for her if she'd been honest with them from the start, and that she didn't even have any real reason to be ashamed.
Played For Laughs: Alice is married, but ashamed of her husband, and takes her attractive and wealthy cousin along to the reunion in an attempt to impress her former classmates. Her real husband shows up, but no one believes he's really her husband.
Played For Drama:
Alice's secret comes out in a most humiliating way, causing everyone to lose more respect for her than they would have lost if she'd just been honest from the start.
The man that Alice chose to pose as her husband happens to be the boyfriend of someone there, which (understandably) pisses that person off.