a sucker for (someone or something)
Someone who tends to be easily attracted to a particular type of person or thing. What can I say—I'm a sucker for romantic comedies! I've always been a sucker for a guy with a six pack.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
sucker for someone or something
someone who is prejudiced in favor of someone or something; someone who is drawn to someone or something. I'm a sucker for a pretty face. Ted is a sucker for any dessert with whipped cream on it. I don't know why I volunteered for this job. I'm a sucker for punishment I guess.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.