To become obsessed by a romantic interest, over-analysing the relationship, especially in the early stages. Focusing way too much attention on this person and letting it occupy your thoughts 24/7. Most commonly occurs in people who have too much time on their hands and not enough hobbies.
Single girl: Oh my god, I just text lover man and he hasn't written back yet! Do you think that means he isn't interested? Oh wait he wrote back, what do you think that means? Should I write back? I should wait 20 minutes first, right?

Friend of single girl: Girlfriend, you've got brain disease over this guy!
by Brooke Harward February 26, 2008
Get the merch
Get the Brain Disease neck gaiter and mug.
When you are infected with SBD you are willing to pay 5X-10X the market value of a clapped out miled out oil leaking rust bucket Subaru because it's got a turbo!!!!
"Jennifer just told me she bought a 2001 Subaru WRX with 300k miles for $12,000! She told me it has an STI motor and a salvage title."

"Wow dude, she's got Stage 4 Subaru Brain Disease"
by Nived67 January 27, 2020
Get the merch
Get the Subaru Brain Disease neck gaiter and mug.