A person with the lobster disease is someone who has the recurring problem of catching feelings for someone after having sex, despite initial intentions of keeping things casual. Once they've shared a sexual experience with one another, emotions unavoidably develop and a desire to mate arises, an incurable side-effect resulting from the lobster disease.
The term lobster disease has an indirect reference to a bit from the television series, Friends, where Ross is upset because Rachel and him weren't getting together whereby Phoebe reassures him saying that Rachel is his lobster. Lobsters are known to mate with only one partner for their entire lifetime.
"Jane can't have casual sex with guys because she always catches feelings, she must have the lobster disease"