sweatdrop
A single large sweatdrop usually used to depict a character who is nervous or embarrassed in a situation.
If the single sweatdrop is small/normal-sized, use small sweatdrop instead.
If the single sweatdrop is especially huge and unrealistic, and appears on the character's side or back of the head (as might be seen in 1990s anime like Sailor Moon), consider using comedic sweatdrop instead.
If there is more than one sweatdrop, use sweat.
