When one of your friends appears to be doing something really nice for you (such as asking you to be in her wedding) but in all reality is royally screwing you. (By subjecting you to months of listening to bridezilla talk, forcing you to pay hundreds for a dress you'll never wear in your life... etc) The word can apply to any situation NOT limited to weddings.
"Wasn't that sweet of Jessica to ask Marianne to go to the beach?"
"Not really. You know she just wanted her to go so that Jessica would look skinny compared to Marianne who's gained a few pounds."
"Wow. She totally got bridesmaid-ed."