I have globally assigned C-c/ to ace-jump-mode but reftex-mode (a minor mode for citations used with AucTeX) overrides this key with some function I never use.<
C-c/
You can use following command:
(define-key reftex-mode-map "\C-c/" nil)
to unmap this function from C-c /... But reftex-mode should be loaded, so reftex-mode-map will available for modification
C-c /
reftex-mode
reftex-mode-map