Yes, this is the reason your driver's side seat belt is missing.

Why? Because Deadpool needed a new utility belt. So, he broke into your car, pocketed your Journey's Greatest Hits cassette, and lopped off your very nifty seatbelt.

Our Deadpool Utility Seatbelt Belt is actually available in two very specific sizes because occasionally, Deadpool enters a 24-month depression that involves an awful lot of ice cream and donuts.

Anyway, this adjustable Deadpool seatbelt belt-- made from actual seatbelt material -- simulates Deadpool's actual belt with illustrated pouches and Deadpool symbols.
 
And yes, the seatbelt buckle is also taken from an actual seatbelt -- your seatbelt, specifically.