Step 1:- Pick a celebrity who will resonate well with reddit community (like Gordon Ramsay, Louis CK, Bill Nye etc).
Step 2:- Find out when their birthdays are. You could refer to http://www.famousbirthdays.com/ if you are running out of ideas.
Step 4:- Post on reddit wishing the celebrity on their birthday and with a picture with a funny/famous quote of theirs.
Step 6:- Profit!! :)