A person who is sickeningly romantic, to the point of annoying all their friends by constantly talking about their relationship/partner or their desire for one. A wetbag is typically female, but can be either single or in a relationship.
Person a: omg Greg is the best like last night he took me out for a candlelit dinner and then took me to a skytop hotel with rose petals on the bed. Like we've only been seeing each other a few weeks but I really think Greg could be the guy I marry
Friend: ugh you are a giant wetbag