I'm sorry I can't tell you the specific name for the fear of mayonnaise, and I think its unlikely that it does have its own name. This would probably just come under the term food phobia. There has already been a question regarding this on blurtit, you can find it here: q836575.html
Oh my god I absolutly hate mayo!! My friends little sister chased me around her house with it and I locked myself in the bathroom for over an hour!! I hate it soo much