Make them feel insecure or inadequate in providing for others.

eat someone else's home cooking....lol!

Flaunt your very happy relationship in front of them.

My guess: Have professional status they do not.

Have gorgeous breasts in your best dress and be a better flirt. Some cancer women will get livid and stew.

If you are obliviously nicer, more comfortable, or more caring towards someone else they are in competition with (read: every other guy in the history of mankind for their emotional purposes.) Cancer men have gotten jealous for no reason if they have severe mommy issues. 'Wah, wah, wah, you love him more...'