This graffiti is in the hospital. The location is always the same but not the way how to get this graffiti. There are 2 small different ways depends on your decision in a previous episode.
First, please get graffiti numbers 6 and 7 before you miss them in the hospital.
After you get both graffiti go from the starting point straight forward to Mikey's / Drew's dad and after the short dialog enter the hospital room behind. Due to the decision in an earlier episode, you have either Mikey or Drew in the hospital bed
Mikey:Listen all automatically dialogs (cutscene) then go to Mikey and sigh his cast.
Drew:Talk with Drew then duel with him over his pudding (does matter if you win or not) and after the short cutscene sigh his cast.
For a visual guide (Mikey) open the spoiler, inside you find my video with all 10 graffiti locations.
*** Spoiler - click to reveal ***00:08 - Optional Graffiti #1 (American Graffiti)
00:43 - Optional Graffiti #2 (Extra Credit)
01:16 - Optional Graffiti #3 (Peer Review)
02:05 - Optional Graffiti #4 (Monthly Masterpiece)
02:53 - Optional Graffiti #5 (Spit Take)
04:38 - Optional Graffiti #7 (Hello Nurse)
05:26 - Optional Graffiti #6 (Venting Machine)
06:53 - Optional Graffiti #8 (A Penned Appendage)
07:57 - Optional Graffiti #9 (Drunk Drawer)
08:41 - Optional Graffiti #10 (Messed Up)