A prolific malaphor contributor, Yvonne Stam, was at the beach with her sister. To prepare for something they were about to do, Yvonne said they needed to do x, y and z. Her sister said she already done that, and that it was not her first day at the rodeo. This is a conflation of “not my first rodeo” (more than prepared for a given situation) and “you’re no day at the beach” (someone not easy to deal with). Given that they were at the beach, obviously the speaker had that in mind. Thanks Yvonne for hearing this one and passing it on.