sucking male nipple
When a character is sucking on a male's nipple, usually associated with cow boy or minotaur characters.
Don't confuse this with the gender-neutral licking nipple. There, the tongue (and maybe some saliva) should be visible. Here, the mouth is actually covering the nipple in a suckling manner.
See also
The following tags are aliased to this tag: sucking_nipples_(male) (learn more).