3 Making my makeshift post-colon parenthetical syntax at least consistent :)
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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.

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): (etymology 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.

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): (Etymology 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.

2 OED usually refers to Oxford Eng. Dict.
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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): (etymology from the OEDEtymonline):

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.

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): (etymology from the OED):

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.

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): (etymology 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.

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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): (etymology from the OED):

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.