prick (someone's) conscience

to make someone feel guilty.

Seeing pictures of starving children pricks my conscience, but I rarely give money to charity.

• match up against
• match up against someone
• matter in hand
• matter of
• matter of doing something
• matter of life and death
• matter of life or death
• matter of opinion
• matter of record
• matter of something
• matter of time
• max out
• max yourself out
• may as well
• may as well do something
• May the best man win.
• mea culpa
• meal ticket
• mealy-mouthed
• mean business
• means to an end
• mean well
• measure up
• measure up to
• measure up to someone