Cameos in movies are always a bit of a double-edged sword.

On one hand they can provide audiences with a reaction of genuine delight when they find a big-name star who was not listed in the opening credits has suddenly turned up on screen to enliven and enrich the film in progress.

The more negative reaction however can see fans of a particular actor howling in anger as some wannabe gate-crashes some other big-name star?s party ? usually with a scene of such gravitas that it completely overshadows the main star?s performance.