Though it has been quite some time since I watched this movie in the theatre, I believe I recall this slip-up.
Eddie Murphy's and Owen Wilson's characters have just been chased from a party and have entered a sewer. At least Owen's character is dressed in a tuxedo, I cannot recall Eddie's character's attire. I believe they then start becoming emotional due to their current situation given that the bad guys are after them. As well, if my memory serves me correctly, the temperature in the sewer is steadily increasing for some reason.
The slip up is simply that, as the scenes of the characters change, Owen's character's bowtie is shown, alternately on, then off, then back on. It appears to be a real bowtie that needs tieing, rather than a cheaper "clip-on" bow tie. As the temperature increases, why would Owen's character unto his bowtie, then do it up, just to undo it once again?
I have not rented the DVD version of this movie (nor do I plan to!) so I am unable to provide a comment on whether or not this slip-up has been corrected in the DVD or if it has been caught in the "Director's Commentary".