I can't imagine putting on a C150 park brake inadvertantly. Since they are invariably useless it probably doesn't even matter that much!
The only a/c I've seen someone put on the parking brake during flight accidently, was in a Robin, but this was due to a complete brain dump on the part of the student.
Checking that there is pressure in the system is the main point in the brakes bit of the pre-landing checks.