More context might help, but "sloppy", in this general context, means (excessively) moist.

A big sloppy kiss on the cheek may have connotations of exuberant affection, often of the sort that might be tolerated rather than welcomed by the recipient. Tending towards being a bit like having one's face licked by a dog. (:-) The connotations are perhaps similar to "schmatzen".

The connotations may be different when referring to kissing on the lips.

Mike hits it 100%. Like being kissed by a dog. Not a bad thing, at least from my dog.

But a sloppy kiss can also come from a human being. Not always comfortable.

ein schlabbriger Kuss

ein feuchter Schmatz

"They kiss sloppy" (#0)
müsste doch wohl "They kiss sloppily" heißen?

Danke für die Vorschläge, hat mir sehr geholfen :)

@Braunbärin Um genau zu sein heißt der Satz "they kiss in a sloppy way" aber das sollte auch nur ein kurzes Beispiel sein um den Zusammenhang zu erklären ;)

... tauschen feuchte Küssen aus ...

evtl.

...oder: Schlabberküsse