First, the meaning, and then, the etymology, detail, etc.
Babaji ka Thullu here means 'nothing'. A negative, comical nothing actually. Negative in the sense that Babaji ka Thullu is a nothing where you had expected something, or should have got something - something good, positive for you - but you got nothing instead. And comical because that's how it's used by Kapil Sharma, who invented the term, and now by others as well. In a way Babaji ka Thullu shows ironies where one gets nothing.
Now, let's get a bit literal (as though there is something to get literal here, all we'll get is babaji ka thullu).
The word Thullu here has no meaning. Babaji literally means grandfather, but is used to address old men with respect. It's also used to saints etc., and sometimes there may be opium/cannabis smokers among saints, somewhat like hippies. Here it's more like a saint only, though it doesn't add anything to the meaning really.
Click for Meaning of Gutthi
It is also said that the word thullu is used instead of Ghanta, which, though fine in meaning [ghanta literally means a big metal bell with a clapper inside, and makes a high pitched noise when rung], has a slang meaning these days which is penis. Ghanta is also used to mean 'nothing' these days, exactly the same as 'babaji ka thullu'.
By the way, one small but important thing here, since Kapil's 'sign' of babaji ka thullu looks a lot like a snake. Babaji ka thullu doesn't really have anything to do with a snake directly at least.
The adult part: Ghanta is a word that is sometimes used for a pen*s, and babaji's pen*s, which apparently just hangs, doing nothing, like a ghanta, and hence the name. So if you keep counting x=y and y=z like mathematics [which isn't exactly simple maths here, it's more literature, or maybe pulp fiction ;)], then you could say thullu means pen*s, but that's not simply so. However, all wouldn't agree with me, and some would even argue that a pen*s is also called a snake and hence the thullu's sign is a snake, as a comment does too. Well, that's for you to decide for yourself. For me, Babaji ka Thullu means.. well, babaji ka thullu!
Babaji ka Thullu here means 'nothing'. A negative, comical nothing actually. Negative in the sense that Babaji ka Thullu is a nothing where you had expected something, or should have got something - something good, positive for you - but you got nothing instead. And comical because that's how it's used by Kapil Sharma, who invented the term, and now by others as well. In a way Babaji ka Thullu shows ironies where one gets nothing.
Now, let's get a bit literal (as though there is something to get literal here, all we'll get is babaji ka thullu).
Click for Meaning of Gutthi
It is also said that the word thullu is used instead of Ghanta, which, though fine in meaning [ghanta literally means a big metal bell with a clapper inside, and makes a high pitched noise when rung], has a slang meaning these days which is penis. Ghanta is also used to mean 'nothing' these days, exactly the same as 'babaji ka thullu'.
By the way, one small but important thing here, since Kapil's 'sign' of babaji ka thullu looks a lot like a snake. Babaji ka thullu doesn't really have anything to do with a snake directly at least.
The adult part: Ghanta is a word that is sometimes used for a pen*s, and babaji's pen*s, which apparently just hangs, doing nothing, like a ghanta, and hence the name. So if you keep counting x=y and y=z like mathematics [which isn't exactly simple maths here, it's more literature, or maybe pulp fiction ;)], then you could say thullu means pen*s, but that's not simply so. However, all wouldn't agree with me, and some would even argue that a pen*s is also called a snake and hence the thullu's sign is a snake, as a comment does too. Well, that's for you to decide for yourself. For me, Babaji ka Thullu means.. well, babaji ka thullu!