Arthur is such a sin-ful fellow, who is always trying to excite any geeky girls with these trig relationships:
a) sin x = x – x³/3! + x⁵/5! – x⁷/7! + ⋯
b) sin 2A + sin 2B + sin 2C = 4 sin A sin B sin C, where A, B, and C are the angles in a triangle.
b) ⌽ = –2 sin 666°—when the number of the beast, phi, and sine are in an eternal triangle.

example 1:
person 1: Hey did u comit a sin last night?
person 2: Yes, i had a one night stand, if that's what you ment.

example 2:

I didn't listen to my parents. Oh, i'm so sinful.

example 3:
I like that hot ass guy with tattoos! He looks so sinful.

"I was so sinful last night that I almost had to change my panties," my friend Jackie would say.

His sinful action caused her to benefit in alimony.