Oh boy, this really is minefield for those who want to get it right! There are so many things which can go wrong so you really need to be aware of what you are doing.
Think about your company. Is it quite conservative or a little more informal? Are your co-workers older or younger? Do you colleagues gossip a lot to each other? Will anything you do be on the internal email by 9am the next morning? Are your secrets going to be shouted out in the office canteen? All of this needs to be considered!
Start by dressing appropriately. Your idea of casual maybe rather more racy than your colleague’s idea. If in doubt, err on the side of caution. Also do ensure that whatever clothes you have decided to wear do actually stay on all night...
Do not get drunk. Stop drinking as soon as you reach the point of tipsy if not before. You will regret it in the morning if you drink too much.
Join in and have fun but do not let your tongue get too loose. Telling everybody your personal thoughts about a colleague will always be a very bad idea.
Just take care!
