“That makes my butt hard” (“making my butt hard-verb version) is an expression that can have slightly different meanings depending on the circumstance, but generally the expression is used in a positive manner. This positive expression can be used in the following ways (however not limited to what is listed):
1) Used to agree with someone.
2) Used to express attraction towards someone else.
3) Can be used to convey a general liking of something, some place, or someone.
Examples:
• These bean and cheese tacos are “making my butt hard”!
•Dude, tone it down with the cologne! You’re “making my butt hard”.
•Girl, You makes my butt hard ….no no…that’s a good thing. No…I’m not into anal play… I guess I was trying to say that you give me an erection, but didn’t want to come across as an agro alpha male.
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi