I'm in the music bizz so I'm around these celebs all the time.
Notables would be a music sessions where I was just in the background:
Nicki Minaj (her ass is unreal, pun intended)
Drake
Common
Passed by Jay-Z
Iggy Azelia
Childish Gambino
YG
Next door at a studio with will.i.am
I mostly work directly with other producers like:
The beat bully
Jahlil Beats
Met Skrillex
Ester Dean
Bangladesh
Clams Casino
Soundave
Kane Beatz
DA Bizness
1500 or nothing
I'm actually use to seeing the celebs, I'm almost famous