"He isn't a real boss until he has trained subordinates to shoulder most of his responsibilities." - William Feather
Are you having a tough time dealing with a bossy co-worker? If so, find out how to deal with the wanna-be-boss:
If you are plagued by a bossy co-worker who tries to flex authority which has not yet been bestowed upon them, then simply confront them in a tactful manner. Let the wanna-be-boss know that your top priority is the work assigned to you by your real boss and if they need assistance or, if they are having trouble handling their own workload, then they should speak to the boss.
Also, make your boss aware of the situation. Often, this type of boundary crossing occurs when colleagues are unclear about their roles and responsibilities; which makes it the perfect situation for management to sort out.