The sound of when you sit and your balls slap down on your legs making a "slappy" noise, or when "doing the dirty".
Guy: Jeez it's hot out here! I've been gettin slappy balls all day!
Girl: Maybe you sould go sit in the A/C so your nuts don't look like an old mans.
Girl: Maybe you sould go sit in the A/C so your nuts don't look like an old mans.
by TheMexicangrito October 5, 2012
Get the slappy ballsmug.