backtrace was indeed the word I was looking for, thanks for pointing me in that direction!
I do the following now
function Base.*(a::MyType, b::MyType)
tr = backtrace()
Base.show_backtrace(stdout, tr[1:2]) # I don't need the whole trace
return dostuff(a, b)
end
which has the advantage that execution does not stop and prints only the interesting part of the stacktrace.