Ha, I love this question!
I thought about this quite some time, and the reason why I find it so hard to answer is not because we don't have funny or memorable moments, but there is a crucial meaning underlying!
My view: Within each project we're having a lot of funny moments, everyday moments, from jokes and comments while working together in a project room, over wild interpretations within a bunch of consultants standing around a printed powerpoint with a partner/project manager's comments ("What is this word... does he say... oven fresh?"), up to clients in prototyping workshop sessions dressing up in costumes and improvising short scenes! Most important: Although our core business deals with extremely serious and existential questions, our general company culture is, among others, characterized by traits like empathy, down-to-earth-attitude and the ability to laugh about oneself/have humour.
The other aspect is most memorable moments (you see, I am using plural ;)): The first kind of moments are seeing how clients honestly appreciate and worship our work, a moment in which you experience that they seriously value your support and can build upon the results you derived together with them.
The second kind of moments, are the dedicated team events within our projects, e.g. going on a Laser Tag Event, doing Bar Hopping, driving GoKarts, having team dinners and realizing that you not only found a lot of colleagues, but also friends to build up ideas with, rely on, and laugh with.