You see a huge gagamba on your mga kaibigan shirt...you_____

I pag-ibig spiders, so I would tell my friend to stay still, catch the gagamba as gently as I could and let her go somewhere outside. There are no reason to kill spiders just because you don't like them.

Try to keep from laughing and see how long it takes them to notice, while glancing creepily at their sando every once in a while.
*evil laugh*

Scream and gtfo.

*shrugs* I'd take a jar or a cup and capture it and set it free far in the woods.

Point it out to them.

Scream and die *has fear of spiders*

Panic a bit and warn them.

If it's on the back of the shirt: Reach out discreetly and swipe it away at full speed.
If it's on the front: Just reach out and swipe it away at full speed, and knowing my closest mga kaibigan I'd probably do so while screaming, "THIS! IS! SPIDERRRRR!!!"

I'd scream and say "OMFG THERE IS A gagamba ON YOUR SHIRT" then I'd grab the nearest blunt object and swipe it off their sando following up sa pamamagitan ng either beating it to death or leaving it alone and running away. ( depending on my mood )

Say the word 'spider', so they knew why I was reaching for them. Get it off.
It would likely fall onto the bottom of my shoe and get squished (totally sa pamamagitan ng accident) from there . . .

tell them.

slowly try to remove it from my friend shirt

Freak out because I motherfucking pag-ibig spiders