When Bean is crossing the dates on his calendar, it says "December 1993" on top of it and 31st falls under the Saturday. In reality, 31 December 1993 was on Friday.
When Mr Bean arrives back into his flat after driving into the mattress truck, he coughs up a bunch of feathers. But you can clearly see that Rowan Atkinson had them in his hand bundled up and just blew them out.
When Mr. Bean re-enters his room after the explosion of white paint, the white footprints and silhouette from Hubert that can be seen look unrealistic. They are precisely outlined.