You could say that they are sloppy: (from Merriam Webster):
not careful or neat : showing a lack of care, attention, or effort
This is particularly appropriate to the case of someone who carelessly spills things on them since it carries the connotation of wetness (eg. mud/"sloppy joe" burgers (which spill their contents on you as you eat them): (etymologyEtymology from Etymonline):
1727, "muddy," from slop (n.1) + -y (2). Meaning "loose, ill-fitting, slovenly" is first recorded 1825, influenced by slop (n.2). Related: Sloppily; sloppiness. Sloppy Joe was originally "loose-fitting sweater worn by girls" (1942); as a name for a kind of spiced hamburger, it is attested from 1961.