Think about who it is that you want to roast. Does this colleague have a good sense of humor? If she doesn’t, you might want to reconsider. The last thing you want to do is alienate someone by trying to poke fun. Just make sure that you’re confident she’ll be able to have fun with the roast and not take it too personally.
Ask your roasting victim what topics are off limits. Everybody has sore spots that would be hurtful if poked fun at. Ask your colleague if there’s anything he wouldn’t want people to use in the roast. For example, maybe he has an alcoholic sibling that tore his family apart, or his weight is a touchy subject. It’s important to play fair in a roast.
Find out information from those who know her better. In order to properly roast someone, you’ll need to know the inside information. Find out funny topics from her close coworkers, friends or family members (as long as it’s okay with the roaster). Her behavior around the office is also a topic that your coworkers will enjoy laughing about (especially if she always jams the copy machine or drinks all the coffee, for example).
Decide how organized you want the roast to be. If it’s a casual function, just have a handful of people prepare roasting speeches and go up one at a time. If you want to get more formal, you can choose a host, buy a throne chair for your roaster to sit in, have a stage and create an all-out event. If your roaster doesn’t want to get too personal, you could have one person from every department come up and roast him about his office behavior. For example, he always yells at the marketing department to stop spending so much money, or asks his accountants to write off silly items on his taxes.
Prepare before the roast, and make sure everybody has fun. There’s nothing worse than being unprepared when you have to make a speech. Same rules apply for roasting. Make notes on what you’re going to say, and rehearse. If you have other people speaking too, check up on them and make sure they’re prepared. Set up the event ahead of time and keep the laughs coming.