What's baba ji ka thullu

Girlfriend: Babaji Ka Thullu is trending. What does it means?
 Boyfriend: It's 'Nothing'
 Girlfriend: Why? Tell me na... please... 
Boyfriend: Arre uska matlab 'kuchh nahi' hota hai. 
Girlfriend: Bata na bhav kyu kha raha hai?
 Boyfriend: Bola to 'kuchh bhi nahi' hota hai.
 Girlfriend: Kaminey, akhiri baar poochh rahi hoon, ek word me chup chap answer de...
 Boyfriend: Ghanta....
 Girl gives him 4-5 tight slaps.
 Boyfriend: Mujhe maar ke tujhe kya mila?
 Girlfriend: Kuchh nahi.
 Boyfriend: Yahi hota hai 'Babaji Ka Thullu'
 Girlfriend: Sweetu, pahle nahi bata sakte the?