“On Danny Devito” is used in a similar fashion to “on fleek”.
It can also be used in the metaphorical sense that you are wealthy and successful.
Danny Devito is quite short and stout, and therefore if your pockets are “on Danny Devito” your pockets are full of cash in the literal sense.

When you're a morbidly obese man who likes even more morbidly obese women, but you're both too fat to copulate. So instead, you have her sit on your face. However, because she is so morbidly obese, she can't reach far enough around to wipe herself, so you end up with a vertical racing stripe of feces on your face. The dirty DeVito.

When you eat so much that you start to get as fat as Danny DeVito, but the more you eat, the more funnier you get, like Danny DeVito

A sex act in which one partner inserts their hand and arm into the other partner's rectum, up through their stomach and intestine, and into their mouth through their throat, at which point they use their hand to open and close the partner's mouth much like a manequin. Usually practiced during necrophilia. Named after Danny Devito, who is of manequin size.

anytime something is neato, devito. It’s gonna be a fucking saying in 100 years.
(created by Hannah Montana)

Can be used as the joke name of Irish president Michael D. Higgins when Danny DeVito came out to say that 'someone told me that the irish president looks like me playing bernie sanders'

The sexiest man alive. Anyone with this name is automatically sexy