The reason carbon can't four-bond is because of its tetrahedral geometry. Even with only half of the orbitals hybridized, one orbital on each carbon atom will still face "away" from the bond.
As it turns out, quadruple bonds, pentuple bonds, and even a sextuple bond have all been observed. Where? Metal-metal bonds in complexes, especially the heavier metals with loose electrons. I believe Tungsten and Rhenium both exhibit this odd behavior.
Hmm so can actually happen just not with carbon, i get why now because of its tetrahedral shape. Also is there any special names for these substances, as well as would you know what the most amount of bonds there are possible?